I have had multiple biopsies of multiple varieties and I would not describe any of them as “hellish”. I know that not every doctor is careful, and or compassionate, I did have a needle core biopsy that was a little painful but I can’t fault the doctor for that, it was the location on the chest wall.
I find that most times people worked very hard to make sure I was as comfortable as possible.
Do you know what type of biopsy you are having?

Do not let comments like this scare you. I had 5 biopsies before my surgery and none of them were hellish. In fact, they were quite painless for me. I had made myself so anxious the day of my first one for nothing. If you are nervous, ask for a Klonipin or valium (I did this for open MRI and even that was not bad. The noise can be a bit unnerving). We all have different experiences.
And your other question was can an MRI make a cancer diagnosis. No, only a biopsy.