While I understand the distaste for Displacement as a melee-capping skill and that it would be preferred to separate the backstep from the damage component, the flip-side to this ask is Engagement just being an oGCD melee skill for the sake of having one. 200 potency isn't that very strong by comparison to the others we have.
There are some utilitarian alternatives that have been proposed, however: having Displacement send you to the position of your last Corps-a-Corps; offloading their damage onto Corps-a-Corps and giving it charges; changing the purpose of Engagement into an AoE skill rather than just "worse Displacement"; and so on.
It's a bit iffy in that regard. When it was announced, I think a lot of us were hoping that it would be a tool we could use to prevent overcapping Mana whenever we were forced to be at range, in addition to movement phases. Theoretically (and perhaps a touch ironically with regards to your post), it also fits the niche you were complaining about with using skills faster than mobs die, since we're meant to avoid the non-enchanted combo anyway. For the most part the cost is low enough that our melee is only pushed back an extra GCD on each use, assuming you can't manage to Swiftcast or slidecast your way to victory.- I take that Enchanted Reprise is meant to fill in a movement-heavy moment? But even at a very low b/w mana cost, is it worth to cast a few times and inevitably delay your next melee phase? I almost never find a good situation to use that, to the point that I actually wish for a rework or something that would make it truly an on-the-run useful spell without compromising your melee phase timing.
That being said, I might find it interesting if RDM was given some kind of Anatman-esque or Umbral Soul-style skill for generating Mana without a target, and we've already seen some suggestions for a Lightspeed- or Triplecast-style CD to sling spells on the go. There's some room to play around with and expand our arsenal.