No one says they're not good or gladiator capable, it's just easier to run a spell cleave or some sort of cheese comp.
The only people running RMPS at 2700+ are long time RMP veterans who are good friends as far as I know.
How ever there are lots of first time spell cleavers who are medicore running at that rating, hence why people prefer it over rogues.
I'm holding the highest rated RPS team in world, and I'd still be playing RPS well in 2900's if my rogue was still active.
As you can see from the team roster, we also have a mage in, and I prefer playing RPS thousand times more than Shatterplay.
You just need to find good casters who love playing with rogues and not with other caster scum. I dislike spellcleaves and I prefer melee/caster/healer, people who don't prefer that style of comp over some kind of double caster healer, just play cheese which isn't even really fun most of the time.