Am i allowed to use the same account i used for the 1s speedrun ? I've not played a single game since so the xp stays the exact same (as a proof) and it prevents from making useless smurfs accounts

You can yes. But also Only one attempt isn't enough trust :) I've got like 20+ alts for ranked runs :P If it ever becomes difficult to make new accounts (cuz it can) lemme know I've got tips for it.

Dw we one tried it easily x) I'm waiting to see if my 1s and 2s runs are accepted to try some other leaderboards :D