Okay, first of, whenever I make a post about League on any site, I have to mention I've been playing League since season 3, and played through all champions, got to know them well, mastered some of them, and have over ~3k games over three separate accounts.
Recently, I started recording and playing games where I take a marksman champion designated for bot lane and play them in Top lane or Mid lane, with fair success. Naturally, I'm up against mages mostly, and fighters in top lane.
Currently, the mages are a problem. I'm not talking about the real mages. You know, what real mages were like in season 3 - 4. Brand, Orianna, Morgana, Lux ... I'm talking the CC-packed, ability spamming, point-and-click or hit-them-all mages. Lissandra, Anivia and Cassiopeia (who have been undeniably been problematic since the mage update), fukken Ahri, Vel'Koz, Veigar.
I mostly play marksmen these days mostly, but don't get me wrong - at separate points in time I was a self-declared mage, fighter, jungler and support main, several times, shifting through roles. I'm not a bad player either. I reached mid-plat this season that I started to actually play ranked, in less than month's time.
I know a problem when I see one. And I made a hypothesis based on the following observation; playing fighters (tanks), marksmen and supports, I find myself asking and looking for advice on builds, core items, gameplay, strats much more often than when playing mages. Hence, mentioned mages require little to no effort to play them effectively, except mash buttons. To confirm that, I surf the boards, this Wiki. In above mentioned mage's comment sections and threads I found little to no discussion on build paths, gameplay and strats. In contrast, marksmen's pages often discuss those, and the theory-crafting is present more often than not for any given marksman in it's discussion.
Check it out yourself; what do the comments say on those mage's pages? They mostly discuss skins, cry how broken a champion is or cry about nerfs.
Are the champions flawed, or is it something else? Crapp item choices or straight forward playstyle?
Personally, my favourite mage is Brand. I love playing against him and playing him. When I play against him I know how to get around his abilities, however, I respect it when he gets a kill on me, when he stuns me or uses my minions to spread conflagration on me. With Lissandra for example, all you got to do is stand aside and have her either lose trades or lose CS, because she can't do both with Q if you are staying away from your creeps. The second you try to do something you get speared, and watch her float away while you are snared. That is, until level 6 and she gets some AP (truth be told she doesn't need much AP). Then she point-and-clicks you, snares you and Q's you for a no effort kill. It's like Mei from Overwatch. Ahri gets around juking skillshots while dealing damage, loads of damage even if you manage to dodge all of her skillshots. Anivia ... Don't let me get started on Anivia. R on enemy location for a split second to get that empowered E to proc. Point and mofuckin click. Cassiopeia gets movement speed passively, doesn't need boots, needs to poison you once to be able to E you to death and also has a guaranteed disable.
Forget about Riven, Gnar, Darius, Swain ... It's these motherfuckers I have a problem with.