What does that even mean for RPGs?
high speed, high stamina
stealth
perception, can see other stealth units, reveal fog of war
tracking (see how enemy units move on map)
ambushing (from terrain, when units pass near u). traditional barbarian tactics: drag them into place where you fight well, and kill them there.
extra damage on ambush, but low stats in a direct fight ("skirmish" bad when goes directly against "heavy" unit)
ability to move through difficult terrain (including swimming)
ability to retreat when attacked in melee (hence skirmish)
raiding (getting extra loot from places)
set traps?
attack stamina & morale. that's what skirmishers usually do: they throw all these rocks on you, they don't do much, but it drains your stamina & morale, and then their heavy allied unit wipes you out.
what does that mean for RPGs? to be realistic, world has to be more than a pretty backdrop for your dmg>their hp bar, as said. Rogues by concept are a contextual thing, they need context in game to operate to "make sense".