I’m going to have to disagree with you on the double stun.
Blitz and ram are on pretty low cooldowns, aren’t really all that needed against most bosses when you DON’T need to CC them (maybe ram for the iframe) and the fact that they’re both approaches makes it really easy to double stun pretty much anything. (and stun stone shield is an option if you really must spec your blitz or ram to non-stun)
Both 2x stun and 2x KD are very easy to spec without giving much up. I mean, you’re giving up the crowd pulls, which are pretty much useless against bosses you need to double CC anyways. Just take 10 seconds to spec those skills before bosses.
However, I could buy an argument for a 2-in-one daze or knockback. The problem with destroyer dazes is that most of them just flat-out won’t work on bosses because they pull first.
Having Knee apply joint attack stun twice would have zero effect one PvP balance, and give a skill that is otherwise not that useful in PvE some utility for those bosses that need specific CCs like the drill sergeant.
As for a 2-in-1 knockback, it just makes logical sense because destro is supposed to be the stongman that throws enemies around. The only skill I can think of that you could possibly slap it on is stage 3 red spin which is otherwise not all that usefull. (Though giving up the willpower buff to do it is a very heavy PvE tradeoff)