My cat was an outside cat and she eventually got hit by a car.
I don't regret letting her outside cause that's just the kind of cat she was, she was very active, liked to explore, was often in my grandparent's home as well.
It was sometimes pretty hard to get her to come inside but for the night she had to.
For such a cat, an indoor life just is no real life, then again, the cat I have now hides under my bed when someone walks up the stairs to the front door, when I accidentally lock him out he waits infront of the door with big round eyes, when I try to put a harness on him he transforms into a crocodile.
Imo it really depends on the cat, there are definitely cats that enjoy an indoor life more, especially if they've grown up in a shelter and not outside, and there are also cats that would suffer if you locked them inside, my first cat was a stray / wild cat before she got picked up by the shelter so an indoor life just wasn't for her.