I don't know why you are trying to pre-emptively excuse this movie and the core reasons for meh. DC has the richest villain/hero stable outside of Marvel and they insist again on going back to the same well so quickly. Being a "Hamlet" is an excuse for laziness, doubly so with another origin story. It's stale right out of the gate.
You have essentially gave up on originality with your line of reasoning with "There is really only a few character archetypes anyway". You're accepting mediocrity.
I would feel the same if it was Superman or Batman. Any C lister is far more interesting right now. It would have very different restrictions and opportunities for originality. If one was to insist on this plot line would be perfect for someone like the DCAU Clock King, Temple Fugate. First 2 minutes sets him up much like Dredd did. The rest of the running time is him absolutely wreaking everyone including 2-3 C-listers who have to come together to stop him preferably not by punching the problem. Bam, you have a list of characters to make cheaper movies from with far less baggage and more forgiving comic feel. If one is a breakout hit then you have just rolled another A/B list proposition.
I highly recommend Falling Down (1993) instead watching this tired Joker movie.
I can see your point about taking on C-listers.
MCU was built on the C-list. I may not have seen as much Joker because I didn't watch much Gotham because it is a terrible show. At least it was the first season. As far as Film Cinema goes I don't count TV because it is a different beast. I might count a Premium Network TV version if one existed, but regular network TV has a way to ruin everything. I don't count cartoons either. Cartoons are another other beast. You're not constrained by reality and you have a better chance to flesh stories out more and be closer to the source material or improve the source material or go whacky.
I only count film incarnation of which the tally is:
Joker: 2 + 1(essentially a cameo) + 1(the upcoming)
Penguin: 1
Catwoman: 3
Riddler: 1
Two-Face/Harvey Dent: 3
Poison Ivy: 1
Bane: 2
Mr. Freeze: 1
Carmine Falcone: 1
Salvatore Maroni: 2
Scarecrow: 3
Ra's Al Ghul: 2 (I think he's in a flashback on TDKR)
Henri Ducard: 1ish
Talia Al Ghul: 1
Killer Croc: 1
Deadshot: 1
Harlequin: 2(including the upcoming)
Deathstroke: 1
Victor Zsasz: 1(upcoming)
Roland Daggett - 1
Joe Chill: 2
Clayface: 0
The Ventriloquist: 0
Baby Doll: 0
Rupert Thorne: 0
Blackmask: 0
Hush: 0
Man-bat: 0
Mad Hatter: 0
Dr. Hugo Strange: 0
Tony Zucco; 0
Firefly: 0.1
King Tut: 0
I'm sure I missed a good one. It's also hard to say who is specifically a DC villain and who is a Batman villain.
I'm not too terribly familiar with Hush, Blackmask, or Firefly. I'd like to see Mr. Freeze and Riddler done right. I don't know if Ventriloquist, Baby Doll, or Clayface could carry a movie. Those could work in an Anthology movie like Creepshow.