Before 4E, NPCs were built exactly like PCs. This made making NPCs a pita, especially when you needed an NPC class to do it, but it allowed the players to have a general sense of how they worked (very few "gotcha" abilities). Breaking them away in 4E made them a lot easier to build and run, but it breaks verisimilitude when a player cannot do something even vaguely close to what NPCs can do. 5E's original design split the difference in what I feel is a good way; NPCs have similar abilities that are "close enough for government work."
The change to spellcaster NPCs wouldn't be a problem if they didn't make specific decisions. They should list "X is a Nth level caster using Y as their casting ability," since this would allow DMs to customize them with different spells. Their attacks should be listed as "Attack [Nth level spell]," so that it's obvious these are spells that interact with the rest of the game in the same way. Based on recent changes and comments, however, it appears that these changes are deliberate, perhaps in an attempt to shadowban Counterspell and other PC abilities.
The change to spellcaster NPCs wouldn't be a problem if they didn't make specific decisions. They should list "X is a Nth level caster using Y as their casting ability," since this would allow DMs to customize them with different spells. Their attacks should be listed as "Attack [Nth level spell]," so that it's obvious these are spells that interact with the rest of the game in the same way. Based on recent changes and comments, however, it appears that these changes are deliberate, perhaps in an attempt to shadowban Counterspell and other PC abilities.