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.

Magical classes on the other hand start very weak. In my opinion for the first couple of levels the actual power of casters--in terms of usefulness--only increases slightly. And while they get more 'mana', often they lack the useful spells. But once you reach the more interesting spells in your lists (5-10 or higher) things start getting interesting. And in my experience the 'power' of these characters will then quickly go through the roof, as they unlock very powerful spells and have the mana to cast them freely. Example: unlocking spells like fireball is a hell of a game changer.

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?