Alright. Let's go over this from your perspective then since you're not even bothering to read.
On opener? Yes. You have to do that within the first 3 GCDs. Otherwise? It's debatable since at times you also might be having to drain your Gauge depending on your Partner in the fight just before burst if you're hitting 80. Optimally you are right provided you don't run into Famine by using it outside of Burst to prep for Burst.
Here's the problem: It didn't change anything from EW aside from adding that nuke. There was no decision making returned back to the player that impacted DNC's performance. The only decision you got was whether you would have to waste gauge through an RNG mechanic generated by your allies during Burst - that's not decision making. That's forced. Tillana either is used during Famine to generate the 50 Gauge, or it's saved until the end. You cannot say that Saber is prioritized over Tillana if you're right at the last GCD of your burst. If you overcap? Well shit, you lost potency and has no reflection on a player's skill handling that. That's bad design. Already on activation of Technical Step we get DotD as is, so we're already going to be pressing the button anyway to dump gauge.
I feel like you're overlooking the core aspect of DNC and arguing in the wrong direction. If you're saying that it's because the player messed up something in their gauge management, which mind, is determined by their own base GCDs and ally attack GCD frequency, that's not their fault. You cannot say that this is the DNC player's fault when they have resources forced upon them by their Partner or the Party if they're already hitting their GCDs and pressing Saber to drain gauge properly. The instance in where you are saying you push out Tillana is wrong because Tillana is 600 plus the 50 Gauge in a whole GCD. That's 60 more potency than Saber draining resources under raid buff. As said above, I will repeat it again: Tillana cannot be left out of burst and at most be used at the end as the last GCD in the burst to make the most use out of potency, Gauge overcapping or not.
Every 10 Gauge overcapped is an 108 potency loss, and there's not a lot the DNC can do about that other than their own GCD and Gauge Management.
I do because I played BRD during that time. RNG Spikes were nice, but let me remind you of something BRD has that DNC doesn't - Resource Generation involving oGCDs. Bloodletter? That's an oGCD that's generated by Mage's Ballad. Pitch Perfect? oGCD generated during Wanderer's Minuet. It felt good because you could continue your rotation without having to manage your GCDs down to the point it is causing a loss because you aren't spending fast enough.
DNC cannot spend fast enough if their luck is too good and they get slammed with resource generation. All of DNC's Spenders are GCD. The difference is night and day. You cannot compare Feathers either because those are self-generated. The issue I am pinpointing at, and that you have glossed over is the fact that DNC cannot control its own Gauge generation like other jobs can, and the fact we've been given a 50 Gauge Generation Tool is not helping matters due to the fluctuation of RNG when paired with a Partner plus an 8-man party. In 4-man? This is understandable because you have less generation sources during burst.
In 8-man it is insufferable because you are taking a loss if you cannot spend fast enough with a 2.5s GCD. I do not know how to make this any clearer.
Edit: One other thing - I did a quick comb over the other jobs, and guess what? They either manage their own gauge by themselves, or have set timers. That makes DNC even more of an outlier and highlights this problem even further. "Sandpapering" something down isn't the point either that you have a tendency to reference. Making a pain point in the job visible is the point because it does not feel good to lose potency you didn't generate in the first place.
