Spellcasters can do anything the shapechanger could do, and then some. Fly is standard fare for a spellcaster, energy resistance or immunity is not a challenge, etc. They will not be able to bypass anything a caster with common spell's wouldn't, are worse at helping the party through it, and can't bypass many things a caster would find trivial. If its something they need in combat, it takes actions to activate it, and they have to sacrifice something else. There are plenty of things they can't do that I think maybe they should, like shift into something smaller. A low level wizard can dealwith being dropped from the sky. Until 20th, unless they happen to have fly already morphed, they can't stop it. There are also numerous cheap items that can give some of their bonuses.
So yes, they are very flexible, but not as flexible as a mage, and make up for it with better action economy(kinda) and unlimited use. It does not take a lot of points to adapt to a single thing. nothing costs more than 4 points unbuffed, so saying that they can only change a fraction of their points still lets them adapt freely, but limites the flavor of what you can do.

The main problem with these kinds of limits is that doing usefull stuff is cheap and cool stuff is expensive.

I'm glad to hear they added cool stuff for the summoner. I've been waiting for complete magic.