Except weaving DA was never a problem because you always had the option to delay it, using DA for either Syphon Strike, Soul Eater or Bloodspiller was dps neutral (until the point where the ability you used DA on didn't crit but the other ones did, but you had 0 influence on that). So you could always delay DA by 1-2 GCDs or worst case use it during your next Soul Eater combo, you had a lot of flexibility in which GCD you would use it on. This could potentially cost you one use of DA under raid buffs but it was 1. very rare and 2. only a loss of what, maybe 40 potency? Whereas losing Continuation is a loss of 260-300 potency.
Continuation doesn't allow for that flexibility, you either weave it after the Gnashing Fang or you lose it and unlike DA you now have to wait 30 seconds before you can use it again, not just until your next 1-2-3 combo. The only ability that allowed for some limited flexibility in case you needed to weave defensives was Burst Strike, because it didn't break your Gnashing combo and allowed for 2 weave slots. Adding Continuation to it removes that flexibility because now you have 1 of Burst Strikes' weave slots taken up by Continuation, leaving you with the exact same problem that Gnashing Fang has.
The problem isn't that GnB has too many oGCDs, it's that it has too many forced oGCDs that can only be used after a specific GCD and in a specific order. All this does it add more frustration to the job if the boss mechanics don't align well with your rotation, they could've literally made Hypervelocity a basic oGCD instead of a Continuation ability and it wouldn't be an issue because it leaves Burst Strike untouched.
The main issue is that you have no choice to hold them. You either use the oGCDs or you weave defensives instead and gimp your damage because they're now unavailable and you just threw away free damage. The only tool that allowed you to hold them for a moment was Burst Strike, which will suffer from the exact same issue in Endwalker.