If everyone and their aunt is running around hyperspecialised in a game, then yes that´s grossly unrealistic, or if players are just using it to get access to higher levels from their starting point.
But restricting specialists from existance is just as unrealistic.
So because you prefer to dump the power level sluglow, you claim that my dislike of UNREALISTIC limits, is unrealistic... How... interesting.
Either you have SOME sort of XP source, or you do not. As RAW limits to books is level 20 and 8 respectively, those are the levels you can have a decent XP source of as long as you don´t specifically go the extra distance to nerf your game.
Nope. The master having a few tractatus extra in a single Art, perhaps her speciality Art, will work plenty well enough.
Eh, no it isn´t because that´s not how i usually play characters, and it´s not how most players here play characters. Furthermore, as i already said, "cherry-picking" usually refers to optimal choices, heavy specialisation is the opposite of that!
Shall we go for a simple example?
All unmentioned Arts at level 1.
Say we want a big scary fireflinger. Ok, your "cherry-picked version" uses 120XP to reach 15 in Ignem and has a Casting total from Arts of 16 for CrIg and 2 in everything else...
Now then, my preferred version, split the big XP chunk between Creo and Ignem, getting 10 in each with 10XP left over. Now you have a Casting total from Arts at 20 for CrIg, 11 for any other combination using Ignem or Creo(that´s 13 combinations) and you have a higher maximum casting total.
Ok then, lets add an Affinity for Ignem to the mix and go a bit more specialised shall we?
Your "cherry-picked" version then uses 140XP to reach 20 in Ignem, for a Casting total from Arts of 21 for CrIg and 2 in everything else... Yes, yes very munchkin i´m sure!
My preferred version, gets Cr 10 and Ig 15, at 55 and 80 XP respectively, leaving 5 XP less used than than with your cherrypick. The Casting totals now ends up as 25 for CrIg, 16 for any other Ignem and 11 for any other Creo...
Ergo, by the very definition of either "cherry-picking" or "munchkin" or "power level" or whatever you want to call it, allowing highly specialised characters is most certainly is NOT it. Because you can always manage to get a more powerful character by NOT overspecialising... However, concept characters that are overly specialised can often be fun, which is why i consider artifically removing them is a BAD idea.