Why is account bound?
I don't like lock myself with just one profession, but this makes it too difficult (or easy) every time I change during a season
Because people play more than one class, it won't make sense to reset your MMR to 0 when you change class.
So, however, I find myself again having a long series of victories (or defeats). Until the value reaches the real one.
For example, i start the season with a thief (25-30 matches) and being evaluated as Silver 1, afetr I go with the scrapper, what do you think could happen?