You'd be in high gold or low plat, maybe even higher.

They use your MMR and SR from the last season you played competitive and base it around there. It takes account in your winning and also your personal performance. You play 76 and constantly get golds with him then your SR will raise because they trust your ability with that character.

There was a video i couldn't find earlier of a guy who won all ten placements and it got him a rank of around 1700. I'm guessing was around that rank the last season he played and it still kept him there, possibly a bronze.

New account winning all games or losing just one will be placed really high due to it not being able to judge you because that account has never played ranked before. The system will place you high due to your placements and hidden quick play MMR and feels that if you deserve to be there you'll stay and if not you'll tank down to where you actually belong.

I still don't know how I really feel about this system, you technically can be punished by being on troll teams, which is why my recommendation is to pick someone you're a beast with and spam them.