A RDM Equivalent to BLM Triplecast

[Mansion]

I don't get the point?
Unless you want to rework RDM's rotation, which is another topic in its own right.
BLM's triple cast is a utility tool, because movement is much more "dangerous" DPS wise than it is for RDM (or SMN).

A RDM can move quite easily if you know how to use your tools and benefit from them.
Corps à corps and Displacement are straightforward. They come back frequently, you just need to "aim" where you want to land in the case of Displacement.
Dual cast : you can freely move during one GCD. Add a Swiftcast (and slide cast on the first GCD) and you have a fairly comfortable window to move with no DPS loss.
Reprise : the newest addition to RDM, a ranged Weaponskill (so it's instant, you can use it while you run). We don't have final potencies but 300 is quite good for its low Mana cost.
So a slide cast > dualcast >swiftcast > Reprise gives you 3 full GCDs to move (7.5 seconds roughly) while keeping DPS uptime. That's enough to cover any distance I guess.

Although RDM's strength is that you can move once every two GCDs so planning your movements is far easier than any caster.

[Archwizard]

I don't get the point?
Unless you want to rework RDM's rotation, which is another topic in its own right.
BLM's triple cast is a utility tool, because movement is much more "dangerous" DPS wise than it is for RDM (or SMN).

I'd argue that Triplecast is also a small DPS boost, since more than one spell in BLM's arsenal has a longer cast time than its GCD, and even one second faster cast time can mean the difference in losing a Polyglot charge.

But I agree, RDM has a lower value of necessity for additional tools to render spells instant for movement phases. Non-zero value, still higher value to RDM than SMN, but significantly less than BLM.

[Mansion]

I'd argue that Triplecast is also a small DPS boost, since more than one spell in BLM's arsenal has a longer cast time than its GCD, and even one second faster cast time can mean the difference in losing a Polyglot charge.

Well, yes in that specific case of course.
But I think it's a broader issue of casters and movement. Each DPS caster has their own strengths and weaknesses on this topic, and their own tools. DPS uptime comes from integrating this element in the rotation too. In a way, I fear that it would be walking the path of over simplifying things. The addition of a generic "press here if you need to move" button to each caster would be a bit underwhelming, wouldn't it?
I like the idea of skill gap being in this kind of little elements (just like "good" RDM will keep using Displacement instead of Engagement and stuff)

[Archwizard]

Well, yes in that specific case of course.
But I think it's a broader issue of casters and movement. Each DPS caster has their own strengths and weaknesses on this topic, and their own tools. DPS uptime comes from integrating this element in the rotation too. In a way, I fear that it would be walking the path of over simplifying things. The addition of a generic "press here if you need to move" button to each caster would be a bit underwhelming, wouldn't it?

I 100% agree -- at least as far as each caster dealing with movement periods in their own ways, giving them their own identities. Otherwise you may as well remove Ruin II and just make Triplecast a role action.
Of course this does mean that BLM is kind of the odd man out in this regard, I think, since its movement has been woefully crippled without popping cooldowns that may also have been used for raw DPS, but hopefully some of the changes in Shadowbringers have addressed that to an adequate degree.

That said, while I do agree with such things as adding to a job's skill ceiling, it's a very delicate balance, particularly when it involves creating new tools where the entire fact of their availability to players can determine the player's skill.
For instance, to use your example of Engagement, while it is a "safer" option than Displacement, it could be considered something of a DPS trap tool by some players (particularly ones who think they're better than they really are or want to copy top-parsers, and will persist in using Displacement instead, continuing the trend out of spite), and "optimal" players will find ways to use it as little as possible (as you yourself have demonstrated); same case with Scathe for BLM. In both cases there have been (already!) cries for outright replacement.
On the flip-side, tools like Apocatastasis were primarily used by high-end players at very specific points in a combat engagement, and relatively ignored at lower points in play (which I expect is technically also true of Addle, save for the new players who think role actions are supposed to be part of their rotation and spam it on-cooldown alongside Drain and Break).
When you have tools that aren't used across all skill levels, it can feel something of a wasted space to one group or another. That's what makes something like Triplecast particularly appealing, since "optimal" players will find creative uses to get the most out of it and everyone else can still get their money's worth without feeling a loss.

[Mansion]

(as you yourself have demonstrated)

I'm still so proud about this lol.

You have a point indeed, but then we enter the debate of job identity and skill gap. Role actions are a little bonus, and using them only makes a difference in challenging content (although a proper timed Apocastasis is always welcome, yet redundant most of the time because the tanks use their own CDs). I'm not sure there's so much to balance there, I like the idea of providing a set of tools and it's up to the player to understand them and use them efficiently. Otherwise, it's either hard to shine with those or you essentially lose the micro-challenges in rotations and individual jobs. I think it's the underlying fear of healers right now, seeing how their kits are getting similar.
Back to casters, I like the idea of having general "Casting challenges" (MP management, movement, utility, burst) but individual solutions, that's what makes a job enjoyable and special in my opinion.

[Gruntler]

So, build up to 100/100 and then your rotation becomes Verflare->Verholy->Scorch, and because your mana is still 100/100, your rotation remains Verflare->Verholy->Scorch as a literal 1-2-3 combo?

Sounds awful.

[KaerisKlyne]

Barring the necessity of similar tank and healer tools, I don't think any job really needs an equivalent to what another job has re: how it gets its damage out because they should still feel different from each other while executing actions for the same purpose. AoE is AoE for example, but I don't want every caster to have an umbral heart equivalent to fire off multiple heavy-hitting spells.

[Sylvain]

Barring the necessity of similar tank and healer tools, I don't think any job really needs an equivalent to what another job has re: how it gets its damage out because they should still feel different from each other while executing actions for the same purpose. AoE is AoE for example, but I don't want every caster to have an umbral heart equivalent to fire off multiple heavy-hitting spells.

It's not properly an equivalent but more a tool for the same purpose (or somewhat)

Caster optimisation, beside the rotation, mainly revolves around being able to keep good casting uptime while doing mechanic. All 3 jobs have different means to do so,
RDM has Dual Cast and Reprise
BLM has Thundercloud proc, Firestarter and Triple Cast as well as Xenoglossy next xpac
SMN has Ruin2 and DWT for instant cast

Some have dual functions (Dual cast is both a mobility and dps tool, so is DWT). But in the context of "uptime" these are your tools and they serve the same function, keeping "uptime"

However in practice they don't operate nor feel the same (thus calling that homoginisation is a bit weak, it's like saying all caster are homogenised because they have casting time of 2.5s)

So I wouldn't say "reprise was introduced because it had no equivalent to Y tool", but more "RDM had issue with extended movement, (as well as overcapping mana), here is a tool to adresse the issue."

There are things all job within the same role need to have to be able to properly

[KaerisKlyne]

It's not properly an equivalent but more a tool for the same purpose (or somewhat)

snip

There are things all job within the same role need to have to be able to properly

An equivalent...is literally a tool for the same purpose.

Each caster already has the tools it needs to do those same things (albeit new SMN is actually a little stricter where movement is concerned if you don't want a big potency loss in output). RDM doesn't need a pseudo-Triple because it has that in Dualcast and Reprise, and if that's not enough, it's time to look at either improving job skill or getting a better handle on fight timings.