That cool and all but how does training your mind increase your physical stamina? That was a straight ass pull by the writers. The thing about Frieza replaying all the different ways to defeat Goku in his head made sense if he was increasing his fighting technique but I don't understand how that made him be able to stay in gold form longer. If Frieza was in hell IN golden form in the coc00n focusing the whole time, then it would have made sense for him to figure out how to be in the form for longer periods of time, but he was in his final form during the whole time.
I don't think frieza increased in physical strength, he was stronger than goku blue even when they fought the 1st time, he just burned through his ki. So him being tortured in hell and mentally training himself for his next battle with goku would really only allow him to manage his Ki more than anything else. His Ki/energy control should be through the roof and we kind of saw that with how he handled that god ki. He escaped, controlled and reused it.
Everything else was just frieza being frieza.
A huge part of characters getting "stronger" is Ki control and growth which doesn't seem to take much physical training but more time and mental training. Vegeta literally didn't go god mode until he learned how to control his ki.