The combatant/sneak may be outshined in both areas, but they will never be powerless in either.
In my opinion, time in the spotlight is not decided by technical abilities, it is decided by GM scene setup and player cooperation. Your combat monster might be very busy slaughtering minions somewhere while the spotlight is on the guy who struggles to fend of a technically superior opponent and protecting a hapless NPC, or a key device - the combat monster does the technical heavy lifting, but the spotlight is not on them. "Moment to shine" is a scene building decision, not a technical one.
On the other hand, not being powerless *is* a technical decision. If you create a system where characters are overly specialised and each action *requires* the specialist to be done properly, you end up with a series of scenes where, each time, some people are busy while others wriggle their thumbs. That's why I don't like the healer classes, by the way (and the Healer class specifically): their area of expertise is purely reactive and not one where you want to put the spotlight on.
Additionally, not having archetypes ensure that the characters can develop according to what they have lived and what they want to do, instead of developing according to what their archetype tells them to do. It's much more organic.
And if you say "but everyone can develop any skill, it just requires more effort for some than others", I think you're missing the point - that's a more like a band-aid on a bleeding wound: it can prevent immediate death, but your patient still requires serious medical attention :p
Honestly, the best RM-like campaign I GMed was the one in which I removed all skill costs and simply provided my players with a list of skills and attributes and asked them to tell me what their characters were good at. Giving back complete control over over character design (unhindered by system restrictions) was the best decision I ever took, because players could think of their characters in terms of background, story and affinities instead of thinking in terms of what they could afford. Doing it collectively ensured that people had the same sense of scale in mind and that expertise niches and overlaps were the result of conscious decisions instead of being by-products of the system archetypes (yes, I also let them mix-and-match spell lists almost at will, providing it made sense in their background story).