RMSS appeals to people who like a strongly structured system that does a good job of managing an amazing level of detail.
RM2 appeals to people who like a flexible, modular game and are unconcerned with balance, power creep, and nit picky details.
I'm not sure you can have a structured freeform game...
I think this is a rather unfair view. RMSS is essentially one fixed variant of RM2. The problem with this logic is that you cannot view "RM2" as all people playing it as playing one big system.
Yes, RM2/C is filled with options, allowing for many differing levels of complexity and power level.
This doesn't carry on to the value judgement that there's no concern for balance or power creep. . .what it is is that it leaves the judgement call as to what power level you want in the hands of the GM. What's overpowered in one game is underpowered in another. . .and if you were playing RM2 and just adding on everything from every companion as it came along, you did experience power creep, but I don't know many GMs who allowed "anything!" without knowing what they were getting into. (And many of the companion rules are mutually exclusive and incompatable.)
As I see it, RMSS is the version of RM2 as played by the GMs and players who happened to work for ICE. . . .
So, we could just have easily gained the same level of top down coherency if ICE had said "We are going to publish LordMiller's house rules as the new singular official version".
By paring off the options, going with a singular set of rules, they made it so you could go from game to game "We play standard rolemaster". . .when in the past it was "We play RM with this and that and not with that and this, and I've changed all that."
I suspect the mistake lay in the fact that if you're going to enforce a single "standard" they might perhaps have been better off doing it RMX like, with a very simple, cut down version. . .rather than choosing to make the standard the most ornate, options activated fully comprehensive version of someone else's house vision of what the game should play like. . . .
Standards should impose a standard of all the items that make every game the same, not impose as standard the most ornate, byzantine, curlicued, down to the nth detail version of one house's vision of how the game should be played.
I'll be the first one to admit that RM2 has lots of warts and flaws, but I'll counter that it's a lot easier to change something you don't like than it is with RMSS. . .presenting most materials as options, with a tiny core, seems to be the best way to satisfy the most people, while presenting a giant, harder to customize "complete vision" seems to have ticked a lot of people off.