More subclasses and subraces over levels. Two main reasons: Implementing quality content for more levels is likely *much* more resource intensive than adding a variant class/race. I still feel confident there will be an expansion to the game taking the main character to level 20. So yeah, both sugar and honey baby!
Wizards are not as powerful in 5e as they were in BG. All spells don't scale unless you spend a higher spell slot, and in this case they only get 1 damage dice per slot level.
Also the most powerful spells such as Time Stop and Wish are severely dumbed down and have tons of restrictions to use.
And the damage a Wizard can deal with spells is easily surpassed by a Rogue or Paladin.
That is a half-truth at best. Wizards are IMMENSELY more powerful in many regards. Low-mid level Wizards were previously crap unless you kept resting to memorize spells, and then they were just barely okay. 5e spellcasters have strong scaling damage cantrips, can cast in full plate armor (and shield with proper feat), have more health and better attack etc. You can multiclass a caster magic missile specialist that can cause 700+ damage in a single round for instance (2 fighter, 1 hexblade warlock, 17 evoker wizard). This is immensely much stronger than any BG-original Wizard from level 1 to 20.
