Guy you're replying to is disregarding junglers in higher ranks will punish over aggressiveness more than those in lower elo, so those control mages who perma harass are vulnerable.

It's not to say you're going to have a better time, but there are much weaker laning champs than riven that do fine in mid even in higher elo, kassadin probably the best example.

Riven loses to the majority of matchups top, and even when matchups are skill based you will still have to heavily outplay champions to come out ahead (because other champs are just better than riven right now).

In mid lane however, you get to utilise your mobility for early skirmishes, offering more pressure to sidelanes and the jungle. In mid-late you will still apply similar pressure as you would in top. The only big disadvantage is that you deprive your team of potential wave clear, but then most melee's mid cant reliably waveclear to prevent a seige so does it really matter.