I would think it all depends on what you are looking to take away from your cruise.
I have been on 2 cruises that had a "singles" group on them, and while I wasn't part of the group, I was invited to all their activities.
Off hand, I would say women to men ratio 5 to 3 at least.
On one sc, about 5 of the people joined my (loosely formed) group stating 'we were more fun"
I'm grateful I saved about $300 on my 7 days.
Many I'm sure are more comfortable with someone else "taking the lead" and organizing things, as well as being part of a "group"
So, it's really up to you.
It's doubtful I would ever join a group cruise for singles, just simply because it isn't a value for me.