If you have read through, you should have seen the comment where Csxstars has said that the reason for the light blade is an injury. If you can't understand why someone with a wrist injury may be helped by a lighter blade, then it would make me wonder.
But who said anyone here was a professional? What does the idea of a 75g blade for a wrist injury have to do with what you are asking about here: "Are you sure the 75g blade is professional?"
Besides, I may like heavier blades. Another person may like lighter blades. But personal preference is personal preference. So, even if it was not because of an injury, if someone likes light blades and wants their blade to be 75g or lighter, why would you make a comment like: "No matter what you say, I don't believe it." I have a good friend who is probably better than about 75% of the forum, maybe more, who likes really light blades (his is 72g) and, it sure does not stop him from being an amazing player. But no, he is not professional either. He is just darn good.