Having only experience with RQ6 (so far) and no experience with magic in any BRP derived games (not even in old RQ or CoC) I can only comment on a very limited experience (sorry about that).
If you compare a combat with ogre against martial combatant (with weapons) and spell user (that might also know something about weapon combat) you have to consider some things. First of all, a proficient warrior doesn't run out of magic points that might not replenish anytime soon depending on the setting. Certainly fatigue can be a factor here but that ogre is as prone to fatigue as the warrior. Spell user casts the spell and delivers the effects (if they are not mitigated by willpower) and that's it. At the same time warrior can use special effects to create interesting tactical choices and ways to make that ogre a non-threat (whether by killing it or using non-lethal ways).
So, without actually using any of the magic systems in RQ6 I have the feeling that there still is a place for non magical characters, even in combat.
My experience with OpenQuest is from reading Company and Renaissance SDK. It really seems to be a bit lighter to run than RQ6 or Legend.
As for other races (demihumans) certainly higher and lower stats affect skills but I don't know how much. I suppose elves should get more skill points because of their longevity but since this is the common problem in all fantasy games (for example in Rolemaster) I would just say that the particular elf is so young that he gets to spend as many skill points as normal starting characters.