MR_SLINDiplomattThe biggest problem is that valve said you only get 1 rank instead of ranks for each classes. This is so bad. For me personally, I'm pretty decent on a few classes and then there are classes I have 5 hours on and can't play for shit.
This is pretty standard for most games these days. They don't give you a separate rank for each class that you play in Hearthstone or each role that you play in League of Legends.
There's a difference between playing a different role like pocket or roamer (I know that's less of a difference than other games but still most people are better at one than the other) and then playing soldier, spy, medic or sniper. Like trash said there are massive differences between the classes. TF2 has different aiming for a lot of classes, different movement which is very complex and a different play style.
A unified rank will just discourage people from trying out other classes because they know they will get destroyed and lose ranks if they do and then next time they play their main it will be too easy for them, which also sucks for the people in lower ranks who end up against player much better than themselves.