I guess it depends what you are looking for? I am not directly answering your question, but explaining why I have not.
Zwift suits my ADD and makes it easy for me to have an indoor ride season. From April to November, my brain can’t understand how I do or would ever again Zwift. But then when I look at my Strava history, every fall/winter I ended up doing a ton of rides. And the ability to mix it up fulfills my whims, keeps it fun. I like the mix of work outs, groups rides, and various races. All with a huge community available. The variety is what I enjoy, and always climb off feeling like I put in a solid effort.
Having not really felt the need to look elsewhere, can any of the other platforms compete with that?
Are you looking for training structure, or just something Zwift-like to hold your indoor interest, that isn’t Zwift?
Sounds like it works well for you. I only use it to train and don’t participate in races or group rides. I’m a loner and solitary person. I usually write out what my coach gives me and stay in the range of prescribed watts for the 1 hour up to 5 hours depending on the day and ride. I do my own thing on Zwift. The other riders around me give me a mild bit of entertainment but I usually have something to watch on a different screen or I listen to music. So maybe Zwift is not the best tool for me. I might check out TrainerRoad and a few others after an upcoming race.