it's not even a question about floyd. it's a question about how that version of marquez would fair against any current welter. it's true however that floyd has the style's to beat marquez even without the size advantage but size made floyd comfortable going into the fight. he even mocked marquez at one point after apparently getting hit squarely in the face. it means that his welterweight frame can take a punch from a lightweight that could not carry his power unto the weights.
Have you even followed the Dinamita's career at all? He spent most of his career at 126 and moved up to 130, 135, and even 144 to follow Pac. Marquez best weight by far was 126. Unfortunately I believe he bulked up to much in the chest and arms and was (1.) Made to look slow by FMJ defense (2.) To top heavy. He should have bulked up more in the legs. As an avid boxing fan and a huge fan of Marquez I can be honest enough to know he would not fare any well against any of the top 10 welters at this time, and would have a difficult time at 140. He unfortunately bulked up too much and in the wrong areas to get back to 135 unless he takes a serious break and lets his body atrophy for a little while. At his age and accomplishments the only things he can look to accomplish now is a 4th weight title at 140 and possible show down with Pac if he gets humbled by either Cotto or Mayweather. The praise you are giving Marquez is to legitimize Mayweather's victory, in which I can say was a brilliant display, but a definite mismatch most of the avid boxing community could see from the beginning. 130 Dinamita vs 130 Pretty Boy would have been competitive and I would give the edge to Mayweather because of the physical advantages he holds, but lets not forget lesser opponents skill wise have pushed Mayweather further.
His two most impressive wins and his most impressive non win came past the 126lb limit. Dinamita beating Casamayor and Diaz at 135 was probably his most impressive wins, considering the movement up in weight and how he won against them. His performance against MAB was clinical at 130 and his performance against Pacquaio at 130 should have won him the fight. 130 vs 130? Floyd spanks that guy. Floyd at 130 was a huge power puncher, combined with the speed and the skill he has now - go watch him man handle Gernaro Hernandez.