Remove speed from zeal and its items
Marksmen should not have any more mobility besides what their kits may offer and boots; kiting should be about range advantage not range and speed advantage.
So many marksman have inherent mobility tools anyways (cait has a net, lucian has a dash, jhin goes sanic on crits, etc.)
In fact, ADCs are the only class in this game that can skip boots altogether without losing much (build phantom dancer in lieu of berserkers greaves) in terms of speed and actually gain way more than what boots could have offered.
Tanks and juggernauts and most mages don't have such luxuries. Defense boots are a must for tanks/juggs no matter what and mages need either sorc/ionians since the main ap/speed item (luden's echo) kind of sucks ass.