Remove the word "ez"

you can report someone for spamming anything

It's not that minor.

It is a minor infraction. Yes, it's a violation of the Summoner's Code, but it's a small violation that doesn't in and of itself lend to a punishment. To quote Riot Tantram...

Yes, it's reportable. Yes, it's negative. Yes, it's unsportsmanlike. Yes, it could help contribute to a penalty.

No, a single ggez by itself, without further history of unsportsmanlike behavior is not going to result in a penalty.

If someone does it consistently, that's one thing. But don't expect to get a feedback message saying a player has been penalized for each and every time a person says ggez.

It's comparable, if not just marginally worse, than regular BM like "nice flash" or "all that effort for me?".

It shows a lack of respect for one's opponent when they lose. It indicates usually a poor winner.

I agree, but in point of fact, there's a fair handful of passable examples of poor sportsmanship. Beyond that, it being disrespectful and ultimately a violation of the rules does not mean that the phrase should just be entirely blacklisted from the game. Especially when, as I said before, there is an innocuous usage case alongside it being a comically minor infraction.

As for the idea that because it is short for Ezreal, then quickly people can learn to type Ezreal's name. Simple.

In a game as fast-paced as League, people will naturally prefer to type shortened versions of Champion's names where possible. Rek, Kha, Ez, Cait, GP, TF, Mord(e), A/Sol, Cho, Kat, Kog...Need I continue?

Let's also consider that some of those shortened names can also have some other use cases besides referring to Champions; "TF", for example, is an initialism of "the fuck", or "MF" being the same for "motherfucker". We don't hear anyone calling to cull those shortenings, now do we?

I can't remember where it was from, but there's a meme that's pretty appropriate;

"Why use big word when many small word do trick?"

I know one of the regulars here has to have a folder or something somewhere with that exact meme...

In a game where a teamfight can begin and end in an eyeblink, people are going to want to be quick, concise, and readable about their communication. Very few people are going to want to type out full names (especially some of the longer ones, like Aurelion Sol, Mordekaiser, or Heimerdinger) when they have the option to condense it into something quick and clear.

So until you can influence a lot - and I do mean a lot, a substantial majority of the community, like a good 80% of them - to voluntarily go out of their way to type out a Champion's name instead of the shortened version of it, you can't expect people to switch to doing so in the hypothetical event of "Ez" being formally banned from the game.