Quoted By:
I don't think what he did was stupid.
He tested dynamax energy for years using the challenge cup so he was confident he could awaken Eternatus without it going out of control. He only needed Leon as a failsafe incase shit hit the fan when he woke it. When Leon didn't show he figured, 'fuck it we tested this for years, this wont fail' and flipped the switch.
There's nothing wrong with him trying to fix a future problem. Call it hubris, but if he succeeded he would be cemented as the savior of Galar.
The staff and Oleana had full right to stop the protagonist from barging into a private meeting. It's not like Leon was being locked in there, they were just talking and for some reason the protag wanted to get in because...where's Leon?