I'm generally in favor of a strong relationship between mechanics and fiction, but I don't see a problem here. In my view, the PC wizard and the NPC wizard are following different (albeit closely related) arcane traditions. By default, the NPC's tradition is not a class option available to players, in much the same way that "red dragon" is not a race option available to players.And what's the in-game justification for why an NPC wizard has re-charge spells and a ton of hit points, where a PC wizard has AEDU spells and healing surges? Why does a PC fighter need a +X magic weapon in order to strike with the same accuracy as an NPC fighter?
When players ask how they can learn the NPC's techniques, my response is "You've got no idea how she does that. If you want to know, you'll have to go investigate." If a player is interested enough to follow up, I work with him or her to define the particular thing the PC wants to learn, then homebrew class abilities that are consistent with what the NPC does. I had this happen once in 4E with a solo NPC assassin who had a bunch of poison-related powers. The PC rogue was instantly enamored of the assassin and wanted to learn his abilities, to the point of going out and convincing the assassin to train him; so I worked out a way to make it happen. (Sadly, the campaign ended before he got to exercise the option.)
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