Pathfinder 2.0 sidestepped this issue by having class-specific feats instead of subclasses. Just pick which features you want dude, no need to be silly about it. And you get a new choice of class specific feats often.
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Mutants and Masterminds (and I think GURPS) sidesteps it entirely by having point buy with all the abilities and stats. You don't even have classes.
Sometimes restrictions breed creativity, though.
Or Savage Worlds where you literally build your "class" from the ground up
Or Pathfinder for Savage Worlds, which is Savage Worlds with Pathfinder classes converted into Edges (limited to one per rank).
FR. My Battle Smith Artificer can suddenly learn the Wizarding arts and summon a spell book mid-dungeon crawl despite most wizards spending their life learning those things. But despite being able to harness the weave into mundane objects, including armor, to enhance them, or create magic items wholecloth, and even create a living construct, I cannot actually create a magic suit of armor and become an armorer artificer, no matter how much I try.
Remember the one rule of D&D everybody forgets, no matter how much Gygax emphasized it: if you don't like a rule, don't use it in your campaign. In my game I allow any and all combinations of classes. I might even allow a Paladin/Assassin, but the player would have to come up with a really good in-world rationale for it.
laughs in WFRP profession progression
Warlock: I promised my soul in exchange for great power.
Rogue: To which great power?
Warlock: All of them. Let them fight over it when I am dead.
I knew a wizard that had traded his soul for favors so many times he was effectively immortal. He never went adventuring any more, just oversaw research in our flying screened tower. Since old age was the only feasible way he was going to die, which would cause a war between all the outer planes over ownership of his soul, no one would cause his death. He was 218 when I met him, and he was over 5000 years old, and a demigod of secrets, when I met him again, because of a mixup we had while inventing portal magic. We ended up 5000 years in the past and I went back to the present, but he stayed behind. Pagiathrakatos was an interesting dude. Got a compliment from a dwarf on his impressive beard.
Do you happen to read Brust? This reads very Brust.
I haven't. The DM that created him might have.
Why does this sound so familiar?
I have talked about Pagy, and Katherine Du'Cithrael on many other sites.
Do you watch D20? Somewhat similar situation in Unsleeping City season 1.
Big John Constantine energy.
Fiend: Look, I'll take what I can get. Can I get the legs? I'll take the legs. She can have the top part.
Archfey: Did you just call the head the "top part"? That is so fucked up.
Great Old One: wait its not called the top part? What do you call the tentacles at the end of the bigger tentacles?
Rogue: Waitasec, how many boons do you have?!
Warlock: I dunno, a bunch. I lost count.