So it is a bad thing that your character becomes defined by the actions you undertake during gameplay, and become good at what you do constantly, instead of predetermining a group of skills that you want to level you up?
Yes. Classes define the PC's personal history and life experience leading up to the point of the start of the game. It also defines their personal aptitudes and general area of expertise and past familiarity & training.
Look, I like classes as much as the next guy, but I can't tell you how many times I've had to restart a character because I got -ONE- freaking skill wrong in my Major / Minor class sets because during the course of the game, I found another skill that I liked better, defined my character better, and wanted that skill to be what defined me. I played my entire Morrowind run through before realizing just how much I loved Enchant, and to this day feel like I need to play the game through again with an Enchanter character simply to exercise that mistake.
This is a personal choice (or a personal mistaken choice); It has nothing to do with RPG game mechanics. :shrug:
In Skyrim, if I decide "wow, this skill is pretty awesome, I overlooked it before" I just start doing it.
And if you want to predetermine those skills ahead of time, there is nothing, and I mean NOTHING, stopping you from looking over the list of skills in the game and determining what bunch of skill you want to focus on and perk in. I know I already am.
But there should be... Player characters of a given caste should have heavy incentives to remain in class, and /or heavy penalties to break class with an out-of-class skill choice ~and unlike in D&D, I would wish that such a skill selection did require a willing teacher; either paid or indebted to the PC.
Just 'doing a new skill', on a whim is quite seriously like deciding one day to take up herbalism and going out into the park and picking mushrooms for a snack.
As an aside: I'm finding it devilishly ironic that the players most often against classes in RPGs do seem to usually treat their characters as a class instead of a role. :chaos: