People are taking that interview clip about "punishing Jimmy" too literal.
It was so clearly just the writers being playful and joking. They didn't ACTUALLY set out to ruin him. They wanted to give him more nuance instead of having him be somewhat "flawless" in previous seasons. They wanted to make him a deeper character. Whether it landed for you is up to your own interpretation. I think the biggest problem was he didn't really do much outside his romance with Kara. Meaning we didn't get to see much of the Jimmy from past seasons. The same Jimmy who gave up ALL his millions to save his friend, or the same Jimmy who literally went to space and back to find his romantic interest and best friend. We got glimpses of that like when he confronted Lex as Lex was trying to flee. But overall his arc this season was learning to be honest and be a better person to Kara. Which truthfully is fine. That's okay to have romance and fumbling someone be your arc. Which while he somewhat succeeded, his ending still falls a little flat mostly due to their not being a guarantee of a season 4. If there was a season 4 guaranteed I imagine lotta the fears about him would be qualmed as he'd likely "redeem" himself in it. Because while Kara had her own thing going most of the season (truthfully she felt more like the main character than Clark most of the time) it was demonstrated in nearly every interaction that she herself still deeply was interested in Jimmy. Effectively making their relationship somewhat the A plot at times. This means that by their final scene it somewhat felt like...both their plots are unresolved because the show CLEARLY clearly lays out that eventually they will hook up. And while truthfully, their ending is absolutely deserved for Jimmy, it was also I think took to literal as well. We see them actively on a date getting ice cream and at one point they even held hands. Meaning yes they are still interested, but Kara wants to take it slow so Jimmy can keep his word. This also means that while yes the roles are reversed with Jimmy chasing Kara instead of vice versa, they are effectively back where they were at the beginning of the season. I think that is moreso the issue with Jimmy's writing. It didn't really go anywhere. Or moreso it didn't go far enough to happily pay off his errors. You don't needa go full on like get them married but maybe just a small scene of one them resting their head on the other, or holding hands or something. Just my two cents. Hopefully in season 4 (which I think seems more likely than not) they are able to make this whole thing better and pay off this plotline. Cause if not I do agree this would be wasted time that coulda been used to develop other things. I still ship Kara and Jimmy, it just coulda been done better to service both characters.