Considering events from season 1 are a major part of the season 3 plot I don't think season 1 is unnecessary. I actually really appreciate season 1. I've rewatched it and liked it better the second time and would rewatch it again. Season 2, while I found things to like about it I do not think it is good television. First two episodes are fine, there's a mix of good stuff throughout, but there's a lot that's poorly written and nothing is done with the ending. That one I would tell people they could skip and I actually wish I had so I could stop wondering why no one asked Jurati for help during the last 2 episodes (and I don't buy that her scanning an anomaly indefinitely is more important that potentially saving the federation - of which she is a provisional member of). I rewatched season 2 before starting season 3 and I'm honestly not sure I ever want to watch it again.