That's just not true.
"Meta discrimination" is a function of how easy it is to enforce. Just look at M+ to see it in action: because any M+ group will instantly have fifty DPS apply, it's trivially easy to only ever pick the best ones. No matter if they're best by 1% or .1%.
The same would happen in 10-man - the higher tank demands would mean that the number of DPS applying to a group increased in direct proportion, which means you are more easily able to only take the best DPS from the meta. Which means everyone else gets left in the dust.
This is NOT a "RWF-only problem" by any stretch.