To be fair, representation in media is nice. Nobody bats an eye when heterosexual relationships are shown, but the media tends to flip out on even the implication of anything but. The point of some people saying "need" is so those kneejerk reactions stop being the norm.
One example was what may have been seen as (if you squint your eyes, subscribe to stereotypes, and still leap to conclusions) a lesbian couple in Finding Dory, and an explicit example was Tracer in Overwatch being revealed as gay.
Do you remember the shitstorm when Tracer was revealed as gay? Notice nobody gave a shit about Torb having like fifty kids? Was it because a character was revealed to be in a relationship (which I will admit does add fuel to the fire too), or because she was gay? If you can honestly tell me the reaction would have been the same (from the detractors, let's be fair and ignore the pro-LGBT fans who raised vocal approval) if Tracer had been revealed to be with a man, then I'll agree completely with you.
In general, there does "need" to be some representation in media, but only if representing anything is necessary. League of Legends isn't exactly the most romantic setting for storytelling, so having an explicitly homosexual character is kind of stupid. And pretty shallow. If a character was made to be just homosexual, it'd be more insulting than anything else. At least Ahri and Eve have reasons for being as sexual as they are. The most that we'll ever get (or should, really), is something more akin to Garen and Kat's "hinted at if you squint yoru eyes and teased by Riot but never actually the center of any lore" whatever the hell they have (some kind of stabby rivalry with some "ooh he's cute" implications I guess?).