So, if you are aligned better with a smaller party. Vote for them.
It’s not a situation where the Tories have a path back into power left. If I wasn’t convinced of it, I‘d be in the „hold your nose and vote Labour“ camp. If you are aligned with Labour as it is. By all means, vote for them.
If labour get a crushing landslide they’ll take it as vindication of their policy offer…which is bad &doesn’t offer PR.
If labour get big a win but Lib Dem’s, greens, even reform perform strongly &don’t have many MPs the calls for PR will start in earnest
If you want PR vote as you would with PR 🤷♂️