Did we read the same deep dive? It looks to me like wizard has 16 different damaging spell lines. You can use your spell scrolls and spell book like any other class to put spells on your bar and completely ignore the new system.
Alternatively, there is a glyph and invocation system that the wizard can use to put 4 glyphs and 1 incantation on the bar (5 spell slots). With these 5 buttons you can cast any of your 16 damaging spell lines.
Press 1 2 3 4 5 get Fireball
Press 1 2 2 3 5 get Ice Blast
Press 1 3 2 4 5 get Fire Volley
etc.
All this system is doing is allowing wizards to use 5 spell slots to cast any of their 16 damaging spells, leaving them 5 spells slots for whatever utility they want.
How useful will this wind up being remains to be seen. I only played wizard to 20 in the open playtests, but I basically only ever used the maximum damage nuke, the harder-to-resist nuke, or the .1s stun nuke (for interrupts).
I think it could be neat, and maybe a wizard who's got all the spell combos memorized and can pop any of their 16 spells will do some cool and unexpected things. It could also be extra button presses for no real reason. I've I'm gonna spend the whole night/fight casting a single spell over and over, there's no sense in hitting 5 buttons each time to cast that single spell.
Anyhow, I guess we'll see! I could have this completely wrong.