Not sure if anyone would read this but Hi, My name is Tri and my ingame name is TriangleOfLove. Bad players? Okay... Quitters? Unacceptable. I don't mind losing as long as no intentional feeing or trolling or intentional leaving the game. Those are not hot and Fernando doesn't like it.
I played all roles but my most proud besties for each class are
+Support: Jenos, Pip, Grohk
+Tank: Inara, Fernando, Barik
+Flank: Talus
+Damage: Dredge, Kinessa, Strix

Shirtless Koga, what's next? Pantsless Terminus?
If I win, I will stop feeding for 2 weeks.

Obsidian skins, cosmic skins and some paintings that have a blue background unlike most of the others (they are not even painting, just a screenshot from their 3D figure)

I think you guys need to add this in one of the first rows on your to-do list. Me, personally already not really a fan of re-coloring a skin and call it a different skin in the store ( Sorry, I don't want to be rude but that is a lazy work) but I can't understand that you have limited resources. Despite that, unfinished art makes the game looks very... alpha and obviously that can't be called a complete product.

I won't ask for a bunch of different skins (or simply just recoloring skins) of a champ in the store but I mean a 2D painting is not that a lot of work, or maybe if you need help why don't you giving out an open contest for available artists to submit their arts for the champs?

Nah, I'm just kidding. You got this, seriously. A professional hard-working 2D artist can do one piece per one to three days.
Bonus: Instead of taking a skin, change its colors and call it a new skin, can you please make something like a color palettes that let the player can customize their skin however they want? I don't ask for those to become to be dirt cheap but it would make the game very interesting. ( even though the player can change the color, the loading arts still appear as its original. This method, however, only legitimately works with not using recolored skins)

Here is a reference from another game called Warframe that they let the players buy colors instead of recolored skins!

I don't know if is possible, just an idea, and I'm aware that it would affect the market a lot if it comes true, but anyway, seeing all finished loading arts is my most desired.
*Edit:Obsidians and cosmics don't even have a loading art...

I think we don't need a downvote button and as I mentioned, a limit amount of endorsement giving from an account to another per day or amount of endorsement that one account can give out per day may help to avoid the issue.
Plus, match-matching is random and everyone can be in a team with a bad player. That's a fact and I think everyone needs to overcome the problem having negative teammates since it happens to everyone. Some matches still can be saved, some matches cannot, that is just it and all you can do is play your best and not giving up. You already accept the result no matter what when you hit that finding-match button so just prepare to deal with every situation. All kind of toxic players, AFKers, intentional feeders and rage quitters deserves criticisms because of their bad effects on other players but you don't always meet them and even if you do, trying your best and not giving up then even if you lost the game, you should still be proud of yourself and maybe you will receive endorsements from others for not giving up and fought like a real paladin

My idea for endorsement is to make it various and specific like "good teamwork", "life saver", "funny", " good aim", or "friendly player". Each player can only hit +1 for one of those to another player once in a match.

I think it would be great if you can add an endorsing button on the aftermatch chart that allows a player to endorse others if he/she think that their teammates or people in the opposite team were doing great in the game. ( And maybe add limits on number of time that this player can do that on the same player per day).

I also hope that you can add an block (or blacklist) button in the game that a person can block (not receive messages or friend requests) someone anytime in game ( like in the main menu, during champion selection or even in a match) I asked this because as far as I know I cannot stop anyone from messaging me (privately) in the game and that would be annoying if someone wanna flood me with spam.

Thanks a bunch and stay hot like Fernando