Spell users have penatlies like less HPs, lesser armor, and sometimes higher cost for non-combat skills, like athletics, etc.
I don't know how many PPs your spell users have, but while non-users can use their skills all they want, any spell use drains PPs. Since we play RMFRP we removed the PP multipliers as it can be an abuse.
So, I think magic would be too powerfull is you could use it all you want, but is not the case.
In addition, compare DPs used to buy spells (3-4 DPs each rank for pure and 6-8 for semis) to non-users skill costs, learning an usual 10 ranks in a level cost 35 DPs (half base and half open or closed ones).
You see only the best case for sell users, like massive hurting with a fireball, but see it in the other side, a good fighter can do a massacre slashing everywhere with no cost, compared with a magician that any 'fire bolt' costs 6 PPs. If you compare with missiles, there is no comparison between a simple arrow with using PPs.
Compare a parry with the use of a 'bladeturn' spell, that costs 7 PPs each use.
PPs are so limited
We are playing RM since much time ago and I can sure you that is balanced.
The question can be answered simply by playing, try to make a complete group of non-spell users (use outrider instead ranger) like a fighter, a thief/rogue, etc.; and try a complete group of spell users, who can survive more easily?. Spell users pay their versatility with their respective
weakness.
So, is magic powerfull?, sure, but a good fighter too, each one in their domain. IMO each character has its function so there is no need to worry about that. Is a merchant powerfull?, no...it depends, for obtain objects or trade are the best, and maybe for other skills like diplomacy, etc., how are the spell-users or the fighters with these ones?, surely not very good.