Yes he is less deserving because of the circumstances. You have the #1 challenger in Golovkin who is by all means next in line for a crack at the title (further shown by his mandatory status). He's campaigning at middleweight and clearly putting in work by beating top ten guys, basically clearing out the division one fight at a time.
Yes the blame first goes to Martinez for fighting Cotto in the first place, but the man did put in work, obviously beat Pavlik and defended the title against other top ten middleweights at the time in Barker, Macklin and the likes.
Pavlik fighting Martinez was legit, again circumstances. You had Pavlik who beat Taylor for the crown, defended it against Taylor, eventually got beat up by Bernard Hopkins and only had the title because it was above 160, and Martinez who had a thrilling fight against Paul Williams and was being featured on HBO, made sense since he was moving up in weight (and stayed there).
Floyd obviously isn't a middleweight, has no intentions of being a middleweight, and hasn't fought at 154 in over a year. He's a welterweight who can occasionally fight at 154 against the right opponents. Obviously if he fights at middleweight against Cotto it would only be because it's Cotto.
So yeah given the circumstances Floyd isn't deserving of a crack at the lineal title. If it was for Cotto's voluntary fight, sure go for it, but since Golovkin IS mandatory and IS the #1 Middleweight challenger of the world, by all means Golovkin is by far, without question, the most deserving fighter. He's the one putting in the work, he's the one campaigning at middleweight. He's been patiently waiting for his shot for years. It's time the man gets the fight, not a welterweight.