Some counterarguments/examples:
{quoted}1) There's no such thing as "too many skins" until the point in time where a given skin cannibalizes the thematic of another skin on the same champion. This hasn't happened yet with any champion. Even Annie, who has 10 skins, the most in League currently, hasn't reached this point yet.
So, suppose that Riot decides to give one Champion five different skins in a single patch someday (however unlikely it may be). Each of the five skins are high quality, popular amongst both the League community and Riot, and do not "cannibalize" each other's thematics. In your view, would this still not be too many skins? It doesn't violate the guidelines you specified above.
- Riot makes whatever skins they want, for many reasons, such as what'll sell well, what they think people will like, and what they actually want to make in the first place. None of these are invalid reasons to make skins, and as such if they decide any of these reasons justifies a new skin for a champion with a bunch of skins, then there's nothing wrong with that. They wanna do it for whatever reason, so that's that.
Aye, making certain skins because they'll sell well and/or because a lot of people can get behind them is only good business sense and keeps the game alive. Likewise, making skins that they simply just want to make is fair, although I'm tempted to say it can lead to negligence of other Champions who have just as much potential for cool skins as others.
Sometimes, I think the Riot team is so focused on pumping out skins for a particular group of Champions (or "the ones that they want to make skins for") that they simply fail to dedicate enough creative resources and/or brainpower to the characters that also have potential for cool and exciting skins. In other words, they forget or don't care enough about some Champs which can lead to a drought of awesome skin ideas for them.
- Everyone's quick to point out champions who get to many skins, but are quick to sweep under the rug champions with low numbers of skins or those who've been waiting a while who actually got new skins in recent memory. Names that come to mind for 2016 include Sion, Poppy, Taric, Tahm Kench, Vel'Koz, Maokai, Lissandra, Kennen, Kha'Zix and LeBlanc, to name a few.
Suppose that Riot stops producing skins (God forbid). Do you think the state in which skins are at now would be ideal? In my view, it would be best if every Champion had not only the same amount of skins, but also the same assortment of quality (i.e. each one has an 1820 skin, 1350 skin, 975 skin, etc.) before League ends and/or skin production stops. What's your view on the matter?
If skin production were to end right now -- that would leave Annie with the highest number of skins (10), while others like Yorick only have 2. That's really great for Annie players, because they can customize their gaming experience very often, but also really unfortunate (and unfair) for Yorick enthusiasts, who have very little in the ways of giving their matches cosmetic variety.
- This whole argument spawns from jealousy over the champion(s) you like not getting a new skin. It's fine to be disappointed when the new skins aren't for the champs you like, but that isn't a good reason to tear down other champions for getting new skins.
Unless I missed the part in the OP's post where he went out and said this is all spawned from jealousy, I think it's uncharitable to assume that's the case. He may actually have very good reasons to support his argument that he just can't put into words properly.