From my experience non-magical classes in Rolemaster, i.e. combat-focused warriors and the like, do the majority of their advancement in the first couple of levels - say 1 to 6. After that the combat stats will most likely have reached the threshold where investing more development points only very marginally increases attack stats, and even that increase is very tiny in relation to the stats the character already has. Example: raising your sword skill from 90 to 94 is just not a very big deal.
I feel this is problematic when magical and non-magical characters are playing in the same group: often I find that for the first 5 levels or so the casters basically have to be carried by the rest of the group, only to be jump-started as soon as the first powerful spells roll in (often level 5-8), after which they totally steal the show.
What can I do to balance the get-powerful-quickly fighter classes against the takes-some-time-to-take-off caster classes?
We use RM2 in the german version which came out in the 90ies through Laurin and then Queen Games. From what I read on wiki this seems to be almost the same as RMC.