What I mean by this, is that you can pick a marksman in any role, depending on said champion, and it would work perfectly fine.
Top: Lucian, Vayne, Draven, Quinn Jungle: Twitch, Ezreal, Vayne Mid: Lucian, Quinn, Corki, Varus, Kogmaw ADC: --- Support: Missfortune
I honestly can't think of another class that can pull this off.
TehNACHO2 votesFighters and Mages, depending on how loose you want to use the term "viable". I see you're including Miss Fortune in there, so very loose.
Fighters: Top and Jungle duh Mid Gangplank, Jayce, Mordekaiser, Pantheon, Wukong ADC Mordekaiser Support Volibear, Trundle
Mages: ADC Ziggs Everything else should be obvious
Nayzumi1 votesFighters can be put in the marksman role?
TehNACHO2 votes
Hue hue hue
Btw, it's ADC role. Marksman is a class.
EDIT: Mileage may vary on Yasuo as well. He used to be considered a "Light Fighter" before Skirmishers became their own classification. As well as that he had a decent amount of his playerbase seriously consider him for the ADC role.
ModWulf Helhammer1 votesHe also was initially intended to be an alternative to marksmen, hence the faster scaling and the strong counters against ranged poke.
Rebonack1 votesBecause you're playing Summoner's RIft instead of Dominion.
If you want Marksmen to be optional on Rift, it would require massive systemic changes.
TehNACHO1 votesUhh, wrong argument entirely (^ ^')
Addressing your argument though, Ziggs and Mordekaiser exist so that a teamcomp does not necessitate a Marksman, at least in the ADC role.
KVbqbFsC8e1 votesThey are required to take towers and objectives. As much of this board loves to complain about the super weak towers, you wouldn't be able to siege them without an ADC or Ziggs. If you put a bruiser in the botlane and thus don't have an ADC, you will have trouble taking towers in close games.
There are other classes that can play other roles, but you will almost always need a ranged autoattacker so they aren't very good at replacing an ADC botlane.