@Edjan Let me answer this in order, 1st: Myuu and her friends are hardcore players, this is a competition and they are there to test their strenght, that is the reason why they fought each other. they care more about testing their strenght than simply helping each other reach the finals.
2nd: While a free for all, players still had to register to participate in the tournament. Flein was called an invader because he didn't.
3rd: Most players are jealous of Taku because he knows the three "sisters" irl. It's the good old "Normies must die" trope
4th
Ks are pure evil, but they are still following the rules, devs can't do a thing against a player that is playing by the rules.(even though they are abusing such rules)
5th: No, players don't know MC is a man, everyone believes he's just a tomboy girl, it doesn't help the fact that the MC is very good at cooking, sewing and acts like a mother to Myuu. So even though the MC keeps saying he is a man, no one believes him.
Lastly: Players don't have more authority than devs. However in this game, events hosted by guilds are pretty much endorsed by the devs. During such events the Guild Officers or event planners gain a level of authority similar to that of a GM, of course only in matters that concern their event.