"This game is excellent but it need a better online system"
"and why this game is still only on Windows and isn't on Mac and Linux"
- Both are probably because the game was originally made in old Game Maker, so its ability to support fancy new features like multiple OS support and modern online netcode is inherently limited.
"and also it would be nice to have a tier list that sort out every single character (for example S tier: C.falcon...)"
- That's only ever determined by the players, not the devs.