Has Usyk ever been floored, even when he was Cruiserweight champion?
Sure without doubt if heavy punchers and hard hitters such as Fury, Wilder and Joshua hit Usyk with a ferocious hit then he will be floored but Wilder floored Fury several times even though Fury floored Wilder even more before beating him twice (I would say 3 times because the first fight was a dubious "draw" by the judges when Fury clearly won).
That remains the only real way Joshua could win against Usyk, the ferocious one punch but you hit the nail on the head - why has Joshua been trigger shy on pulling that powerful right punch ever since he met Ruiz for their first fight? Something does not add up because he was not even going for it against Usyk instead he wanted to trade jabs because he had success with it against Ruiz II but completely failed him against Usyk. Just as you, I also saw no game-plan from Joshua in that fight.
Just because he beat Ruiz II he became overconfident again and asked to fight Fury but that was his downfall. Now his whole career teeters on the brink of the Usyk rematch.
I see no reason to give Joshua any benefit because Usyk is technically the better boxer, it is unfair to compare the Ruiz rematch with any potential Usyk rematch because yes it is true Joshua dominated Ruiz and won on points in the rematch but Ruiz was overconfident and overweight going in to the fight already having beaten Joshua and did not fully train - as he admitted later.
Yeah, it was a completely different fight. Ruiz looked like he gained quite a few pounds on the night, and also didn't look motivated at all. Plus, Joshua while he did box quite well, avoided any fire fights, and to be honest I think Ruiz has ruined Joshua's confidence in those tight spaces, which actually resulted in Joshua losing against Usyk.
Joshua has always been a fun fighter to watch, not because of his technique or his technical ability at all. We watch Joshua because he always has a chance to knock someone out, and the majority of the time does just that. Now, he looks reluctant, and I'm not even sure what his game plan was, since he walked into that ring, and tried to outbox a boxer he knows is much more technical than him.
The thing is I'm not convinced that Usyk is a heavy puncher at least not compared to the rest of the division, so I think if he can regain that confidence, and risk it like he did against Ruiz in the first fight, he'll end up knocking out Usyk. However, if he approaches it with the idea of showing off his technical ability, he'll get out pointed once again.