I don't believe there is ever a time where the melee DPS had to peel off the boss immediately to deal with the add so the idea of Onslaught being useful in that regard is still something that can be strategized around as it already has been. I don't ever remember Plunge being used in that regard and seeing as how you can simply sprint tomahawk and quickly spin the mob, it seems like a non-issue. What's worse is that more often than not, you're probably going to want to be in Defiance for progression add picking up and that half gauge cost might just nullify your ability to even cast Onslaught if you're unprepared. That ontop of the fact that WAR can't contribute to destroying the add like a DRK can immediately after snapping it makes it more of a nuisance to even stance swap, but ofcourse we can atleast provide the marginal gain to DPS for the SAM/NIN because our Slash is on our second hit right?

And yeah, losing 2 Fell Cleaves for one Inner Beast, and worst off potentially a Infuriate for the unprepared or the loss of Beast Gauge due to needing to hold it doesn't compare to the easily recoverable mana DRK enjoys.

PLD probably still sucks if SwO is still on the GCD but y'know, you can cast Sheltron and then ShO whereas a WAR can't IB then Defiance because that's just FC. And if you FC, you won't have IB on Switch. Better Unchained, woops now I can't Inner Release. But IB woops now I have to delay my Zerk/IR. Better stance swap, woops now I have access to no WAR skills.

Cost? Fair. This steep of a cost that messes with my gameplay more heavily than Grit/ShO ever will? Gee, thanks.