One needs to remind oneself of why RM2 went to RMSS. Because of the power creep inherent in add-on products. People like to make the new stuff more appealing, so they tend to be a little generous with the spell level and DP costs.
I think that even the Essence Companion warrior mage is balanced towards the player. The lists are nice and the DP costs are better when compared with the other semi spell users (who get the bad end of the stick in that department mostly).
Never allow cross system professions, before someone asks to play an Arcist, Power mage, Wizard, Force mage, Sage (yes they were pretty overpowered), Shaman, Malignant, Magus, Crystal mage, Beast master, or Necromancer. When talking power creep, you're seeing the culprits right above!
That said: playing RMFRP, stick with FRP. Whats wrong with assigning a dabbler (one seriously sweet profession) and perhaps adding something like the combat ways and warrior's weapon to the baselists, at the expense of 2 others.
FRP assumes professions to be general avenues of development and the Dabbler is the semi spell user for Essence. None combat geared, but it could be adapted by switching some base lists with either open and closed lists, or (A GM can do that
) baselists from a different booklet.
Coming up with all new DP costs, in the end, will be unbalancing as well. You don't know the algorithme the makers used to balance the costs. You'd be guessing and if you were me, you'd low ball the values and make the DP costs too restrictive, and if you were trying to do your player a favor, you'd underestimate the effect and screw the other players by handing out too strong a profession. While there is nothing wrong with that, it will be bad for GM reputation; which ultimately is what the game runs on.