This doesn't seem like breaking the sound barrier, however, that isn't important since there would be no reason why he wouldn't be MHS due to downscaling.
Same reason as mentioned before, there wouldn't be a reason this would be an anti-feat.
We can see Shen and Andy (Andy does react slightly) having trouble reacting here, Billy is unknown. He has been shown not to care about getting damaged due to having Undead. This would also apply to the revolver as he is nonchalant about getting shot, he barely acknowledges it.
This is possibly due to the nature of Unstoppable, the speed it gives the user varies but I can agree this instance is slightly inconsistent. Furthermore, Andy can react to it, the problem was the force of the kick, Fuuko however could not react. For the final scan you showed here, I have 2 major problems. First of all, Andy again did react to it, but due to it being a surprise attack from around the corner, so he didn't have the time to dodge. It also seems to have been activated in advance as the bullets were already in the air by the time Andy went around the corner. The second problem I have is your "he also admitted beforehand that Top would be the one to strike him". The scan you've shown explains that Andy is vulnerable to Creed's gun due to the sheer force of the bullets, then explains that Chikara and Top are better candidates as Chikara can stop him and Top has the necessary movement speed to strike him while he's vulnerable so those two would be better and Andy would be better off somewhere else.
This part is untrue, Top has something every other character doesn't, movement speed which would allow the necessary attack to be performed. I do partially agree with you here however, movement speed should be separated from reaction or it should be clarified that the speed mentioned is reaction/combat.
I don't think this is a fair point. Tesla has Untell which can create an invisible barrier that stops attacks. This is also a version of Tesla whose interpretation we don't really know about. We don't know if this is sound or not.
Tesla was surprised that Juiz deflected one of Billy's bullets at point blank, not simply reacting to it. For the Billy scan, Andy looked at Billy, he was capable of reacting to it. Even if you do try to say he wasn't, this would still be a surprise attack so it isn't a good example of an anti-feat.
What I do agree with?
I agree that speed is inconsistent and the verse requires a rework. Bullets are a tricky subject in the verse as they would be in One Piece. Some weaker characters like Fuuko earlier in the series should not scale, the same goes for some of the current characters. I still believe that as shown with Andy, top tiers and some other characters should have at least MHS reaction.