I started DMing with 3.5 and later Pathfinder, and I have to admit that edition had swung the pendulum too far in the other direction. Generating the simplest monster took a while (and character creation itself lasted half an hour for a level 1 character, compare that with 5E's much more streamlined process). That said, I think you can keep verisimililutude without requiring the monsters to be built with the exact same rules. For instance, NPCs of a certain race don't need every single racial trait that the PCs get, but a few emblematic ones are enough to give the sense that this is an NPC of a specific race (think of Elf NPCs getting Fey Ancestry).
Hell, pre-3E editions also built monsters and PCs with different rules, but they clearly had verisimilitude in mind when designing monsters. Except, the verisimilitude didn't come from designing every aspect of the monster with the same rules as the PCs, but from adding entries to the stat block that show the monster's logic in its world. Think of the entry notes like Intelligence Level, # Appearing, Day-Night cycle etc. These clearly painted the picture of a world where monsters had ecologies and lived their own lives when they were not being fought in an encounter. You can clearly have this while designing your monsters with different rules (hell, AD&D monsters didn't have any ability scores!). But they need to follow the fundamental logic of the game universe. In the case of spellcasting, that can mean using the same spell slot system (or at least also having a list of spells that they'd reasonably have alongside spells designed for combat effectiveness) and their spells interacting with the magic system in a reasonable manner. The new spellcasting blocks go against these assumptions by (1) really reducing the spell selection and (2) having spells-but-not-spells that break the magic rules. I can almost tolerate (1), but (2) is what really grinds my gears.