I also believe it will die soon anyway cause I had to cut the roots a lot to fit it into my miniature bonsai pot even though I don't think it's meant to be a bonsai...
You are answering your own questions.
If it's not adequate for a bonsai, if the rootball was big and healthy, if it looks happy, you shouldn't slash it down to fit into a mame pot.
You should have done the opposite: plant it in the ground or in a big colander, let ig get used to its new surroundings, let it grow for a season, and use this time to study, think about a good design, train your wiring skills.
But now, now it's too late.