I sort of agree with the OP when it comes to AP, although there's one thing that confuses me.
You said that Boros wouldn't scale to Garou due to Saitama viewing him as a human, with him even wanting to fulfill Tareo's request, and also due to the fact that Garou tanked Consecutive Normal Punches, while Meteoric Burst Boros did not.
I disagree with this, as there's evidence showing that Saitama didn't use any fixed strength against Garou until he turned Cosmic.
Garou was able to tank Consecutive Normal Punches, but right after got one-shotted by a Normal Punch. This implies that Saitama was heavily holding back, even beyond the level he uses to kill every monster he's fought so far.
Because of this, we can't claim that because Garou tanked Consecutive Normal Punch, that he's more durable than Boros. In fact, Armored Boros should be just as durable if not more durable than Monster Garou when just comparing how they took a Normal Punch.
This leads me to my next point. Since we know that Saitama didn't use his Normal Punch strength against Garou until after the Consecutive Normal Punch, we can say that Garou matched Saitama's real Normal Punch strength
here.
But again, this does not mean that he's superior to Meteoric Burst Boros. There's nothing that implies that Consecutive Normal Punches is superior in AP to his Normal Punches, just that they have vastly superior speed.
I don't think Boros got turned into mush because of the raw AP of the punches, but because there were so many thrown at him at such high speeds. We see that Boros can take Normal Punches in his Armored and Released state, so him getting mushed in his Meteoric Burst state does not make sense with the knowledge that it doesn't boost his AP.
Because of this, wouldn't Boros' durability scale to High 5-A? Or at least a possibly rating?