No I agree cs is important. Lux and Morgana are both very good in dom. I just don't think Riven is all that good. She's tier II dom champion in my book, pretty good but not the top tier yet. Maybe I just haven't faced any good Riven in dom yet, that's a possibility.
For bot lane, I prefer champions like Teemo, Malzahar, Zyra
Riven isn't the best that's for sure, but the way i play her makes the enemy botlaners life hell, i rush a tiamat/hydra, push them to the turret then auto farm creeps when they spawn, then go harass them under turret since it takes riven maybe 1 ability and 2 autos to clear a bunched up wave, it ends up with me getting free farmed, while the enemy losing his turret while getting chipped down, meanwhile i'm lifestealing off creeps between each assault.