I maintain a win rate above 50% but sill in bronze

you will drop back. its how the system works

If you play in a party a 50.1% winrate may not be enough to climb because you have an advantage by being in a party and maybe by people above bronze being in the party, or at least above bronze 5. The matchmaker takes that all into account when giving points.

Also climbing doesn’t happen after a small number of games. It’s not like the moment your winrate hits 50.1% the devs just give you GM#1. If you already tanked your MMR to the very bottom by losing hundreds or thousands of games over a lifetime on the account you’re going to have to get around that many wins more than you lose before you make it back to silver 5 or so, and then go from there. More if you play in a 5 stack or other large party.

Didnt someone try it and ended up progressing from bronze after maintaining somewhere between 60 - 68% winrate?

Overall having 50% should stagnate and having only slightly more also stagnates since the more you play the less you gain per win. Hots has a terrible system for that, cant really help it.
To progress you have to have much higher winrate.