I wouldn’t find this so bad, if the mage can make up for this with crowd control or massdamage spells that have an impact on even more powerful foes. I also found the explanation in earlier D&D solid , that mages need to travel with fighters and other group members in the wilderness because they require protection, as they would use up their spells alone rather quickly and are fragile as well.
But yeah, giving the mage the potential to kill foes one on one to greater extent would be perhaps more dynamic, if made good, that is. I only know that for example in Dragon Age, I didn’t find it very appealing. But that can have other reasons too.
As long as skills, stats etc. have still a great impact, perhaps I would be ok with that.
For me I guess it’s most important how it is explained in the game. If the inner logic of the game can coherently explain me why a fighter is equally powerful as a mage at every level of experience, fine.