Marksmen with mobility have always been really REALLY good against melee top laners that lack gap closers, CC and burst. Vayne and Quinn are the 'standard' top lane Marksmen and they murder the living shit out of most melee top laners. Vayne even has true damage to ignore whatever armor you build, a mobility skill, and a knockback incase you get onto her twice.
Yeeeup, working as intended. Most Marksmen have never really been 'weak' in lane, they just go with a support to stabilize the lane so they can get as much gold as possible.