No doubt that at 154 Mayweather would kick GGG's ****** ass so hard that GGG's mother's jaw would need an ice pack. GGG possesses 1/10th of the boxing skills of Mayweather and 1/10th the experience as well. As usual, after get his 154 lbs ****** ass whupped, you would be whining that GGG was weight drained and that Floyd bytched out and forced him to come down to 154. :yep
The only reason Floyd would fight GGG at 154 would be if GGG were a draw on the level of Canelo, and he's not and won't be before Mayweather retires... especially with opponents that would increase his draw unwilling to fight. It's an interesting fantasy matchup, but it's just that: fantasy. I do think that GGG's power and skills would give Floyd a challenge, though, but not an insurmountable one.