Well, the problem is that it seems utterly pointless to put effort into writing a sheet if we have a 6/7 chance of being told that we were allocated a different class and need to write another one, and being required to write a servant that can fit 3 or 4 classes minimum severely limits which heroes can be chosen (and, mostly, limits us to more OP heroes, since they tend to have more abilities and, thus, more classes). If Magos really wants to do it that way, he should tell us our class before we write the sheet.