cait is a good character to learn ad because she teaches laning fundamentals that all ads use. her kit isnt front loaded with dmg like mf or draven who just blow their load and wait to do it again, but rather in range and zoning, which aren't good if you don't make good decisions. like those are the two main things ppl trying to learn the role need to get before they move onto more particular kits, that and the last hitting/harass minigame. playing a champ that literally gets kills by surprise isnt a good way to learn i think
i wouldnt reccomend ashe atm since her main thing right now is her ult. she doesnt really get a lot of mileage from her slows with the meta, like I'd probably rank her as one of the more difficult ads to play, with a kit that does not translate very well to others in the role.
the idea that mobile ads will stunt your learning of the role is so diesel its the chronicles of ridic
if you try to learn ez, you learn skillshots which translates to otter stuff too
this is how I would rate learning wise:
mobile: lucy and ez, lucian gets you a good handle on one of the most popular champions that you will go against and ez gets you a pokey champ that falls behind if you suck at laning
supa carry: vayne and jinx, vayne has great reward for smart decisions and teaches you how to fight for scraps early on when you don't have a great early advantage, jinx also ramps up late, her q teaches you 2 ranges. also twitch
aoe dmg: mf and graves, mf is especially good in solo q and has a kit that has uses in different situations, like her e actually can be leveled now, same with graves who has a kit that's pretty fukkin versatile, his w is good w/ objectives, his q is good for waveclear, but he's another guy that can't really afford to fall behind, i dunno about mf