I don't know who needs to hear this but... player character classes generally should not be used to create "Monsters", nor even NPCs.

Player classes have extraneous information/options that, while needed for playing out the life of a character who is always in the spotlight, is not needed to play out the limited screen time of NPCs/monsters. Creating "false/trap options" for DMs and generally just making them harder to build and run.

Furthermore, monsters and other enemies of the players aren't designed to do the same things... enemies are generally constructed to have, I forget which way it goes, more hit points and less damage(?) (or is it more hiring and less damage) than the analogous player classes.

Bottom line is, a monster/NPC constructed using player class rules will often under-perform.

Lastly... D&D is a collaborative storytelling game. Expecting the DM to create one story based off of 4 or 5 or 6 different, disparate characters (like, by creating unique villains for each one) is expecting the DM to do more work than they should have to do. Collaboration in D&D, in this circumstance, looks like the 4 or 5 or 6 players creating their characters based around the DMs one story-premise and their one villain. To not collaborate in the latter fashion is a large party of what drives DMs to burn out. It's expectations like this post - whether pushed by players or the DM themself - that create our persistent DM shortage.

Basically, as a DM I have a problem with every premise of this entire post.