I can’t find a list of dr strange spells but the marvel fan wiki lists “spells we have seen cast” as just under 150.
If I assume strange knows all that is more then a 20th level wizard who know 84 plus 5 cantrips
Oops. Forgot a link.
Spells and Phrases
The point is Dr. Strange casts whatever he needs to cast. There seems to be very little limitations on what magic can do. The magic is easy with very little downside unless the plot calls for it, which is the exception not the rule. He can spam magic at will, etc.
It's much closer to the D&D Wizard than wizards in most fantasy stories.
Wizards in D&D
1) can cast spells that cover a huge area of influence -- direct damage, all elements, mind control, long range transportation, fly, summoning, divination, shapechange, stealth, ensnarement, etc. You are lucky if you get one or two of these in many fantasy stories.
2) basically no personal downsides to casting. In many stories people age dramatically, slowly turn to stone, get so fatigued they are basically incapcitated, etc.
3) can cast very frequently. In many stories, powerful magic is more like rituals and can take hours or days. Even if not, some spellcasters cast 1-2 spells a day not 20. Gandalf was not prolific. I don't remember the Wizards in Dying Earth casting that many spells per day either.
4) cast very powerful spells. Not only can teleport, but can do it over great distances and take other people with them, etc.
It's top tier superhero like, like Dr. Strange or mythic. Which is the issue when comparing to maritals.
Personally, for an RPG I think #1 is the real culprit. If Wizards were limited to area effect direct damage and say 1 area of influence outside this (transport, mind control, divination, battlefield control, etc.) then things would be a lot better.