I'm not sure which cruise lines you've been on solo. I've been on Carnival, Princess, NCL, and HAL solo. Carnival and NCL seemed to have more activities, to me. For dinner, you can always ask to share a table on NCL. That's one great thing about open dining, you get to meet more people that way. I met most of the people I hung out with on excursions. At least I knew we shared some common interests.
I guess, being an only child, I just don't think much about going solo. I've always had fun because I'm on board. In fact, sometimes not having someone griping is much more fun. Plus, I don't have to worry about doing what someone else wants to do when they want to do it