It seems there are already multiple posts that cover this topic in different ways, but I see the same problems in Zwift that I see with normal road riding. It doesn’t work to just jump on the bike and hope you’ll run into people that want to ride the same way you do. Fitness is just part of this and I don’t think grouping people strictly by w/kg is the answer. Some of the grouping could be done based on new settings in your profile and some could be done based on asking a few questions at the start of a session. Some days, I might want to jump into a group ride with stronger riders where I’ll be holding on for dear life and I expect to be dropped. Other days, I might want to ride solo and just do some easy endurance or tempo.
You could spice this up with scheduled group rides, starting at the local island bike shop at different times of day. Even if you can’t make the start, you could jump in on lap x when it’s convenient.
I’ve only been on Zwift a few times and I think the core technology is great. The #1 thing I’d like to see is a better way to pick my type of ride when I sign in.