I really don't see it as a problem. I mean yes, you can min-max to your heart's content, and players always will. It's irrational to expect a player to create a character that's less effective *in the areas the player considers important* than what he has in mind. But the price is always paid in the end, by the things that character simply cannot do well. With the range of skills available in RM, no one learns EVERYTHING they need to know.
As an example, take the Warrior Mage. Sure, you can make him nearly as effective in combat as a straight fighter. You can even make him simultaneously able to hold his own against the combat spell casters. But the price of that is he spends so many DPs on combat skills of one type or another that when the battle is over he has nothing to do. He's not any good at looking for secret doors, he's not any good at assessing the value of treasure, he's not any good at figuring out how to get back to the surface without having to face the monsters you just outran, he's not any good at tracking or cooking or a dozen other little skills a party needs.
Nearly all the variants available in RM are *possible* to create by careful spending of points in the parent profession. All ICE has done by including Magents, Caveliers, et. al. is place guideposts for tweaks commonly enough desired that GMs will often find their players asking, "How can I make my character able to _________?" If a player wants to create something midway between a Monk and a Warrior Mage, I have no problem with it. But my players all know that I WILL have my pound of flesh in payment for that, sooner or later. The lower cost for skills applying to combat spell casting will translate to higher costs somewhere else, somewhere the player didn't *think* was a priority until he found himself far from town trying to survive without those "low glamor content" skills. It all evens out in the end, so in terms of min-maxing for advantage there's never a "winning formula". Like the Warrior Mage, the compromises the player chooses give him the advantage in some specific areas, but always and forever give him disadvantages in others. Meanwhile, the player gets to play *what he actually chose* instead of merely close enough to keep him from grumbling.
If your players aren't feeling those disadvantages, perhaps you should put them in a scenario where the research and academic skills that no one ever learns suddenly become vital to his survival and/or success. Or take down their Druids/Animists/Rangers when they are far from town and low on food and water. Eventually they'll realize RM simply doesn't allow for a "one man adventuring party" and start tweaking characters for their usefulness to the *group*.
I had a Warrior Mage/Monk cross in a game once. If asked what he was and what he did, he replied, "I'm a dancer. Oh, and I also do special effects." His battle cry was "Five, six, seven, eight" muttered under his breath.
