Having promised myself that I would never get involved in forum debates (lessons from a wise plumber friend), I don't know why I am putting my opinion out here..... probably in Joe's defence??
Speaking from personal experience as (previously a regular but lately an occasional) grp 1 rider -
Group 1 seems to be so straight forward and uncontroversial (although it hasn't always been like that!!). You turn up and know exactly what to expect - a hard ride in a small group, pain, some tough turns on the front, a sprint home, tea and cakes. If you turn up and have a bad day, fall back slightly, lose touch on a hill etc, then because the group is so small it is easily noticed and a call comes to regroup. No bad feelings, no moaning and no guilt trips. Similarly, those feeling that they are holding the group back (due to hangover, lack of training or whatever) will say "carry on guys, I am going to do my own thing" - no bad feelings, no moaning and no guilt trips. Simples! Having said that, it is still a social ride - some talking does actually go on (when you are not gasping for air).
On a few occasions I have started with grp1 and found myself struggling with the pace, so as we have passed the next grp down I have told grp 1 that I am joining grp 2. On both occasions grp 2 was certainly over 20 strong, probably nearer 25/30, and the difference in abilities was enormous. In my view there were far too many riders in the group for everyone to be safe in traffic. The slower riders were struggling to stay with the group (especially on inclines) whilst the faster riders were constantly waiting up. With the numbers so high, it was impossible for those at the front to know whether all riders were "on" so splits and gaps were constantly, but unintentionally, occurring. This in turn makes it very difficult for other road users to pass.
I guess my point is the same as most other comments above. A social ride can still be a social ride with only 6 to 8 riders, and it is far safer too.
If we had (say) 7 groups of about 6 to 10 riders, aiming to average (say) 20,19,18,17,16,15 and 14 mph respectively, every rider could find a group that would suit their precise ability, meaning the group could work efficiently, sharing the workload, and every individual would get equal training value from it. If a rider wants to test themselves they can step up a group, knowing that it isn't such a huge step (rather than the current step up to grp1). Similarly, if you want a slightly easier day you can step down a group, also knowing it wont be
too much easier. It would be easy to keep tabs on who is off the back and far less re-grouping would be required (as everyone is similar ability). There are enough people out there with bike computers, so someone in every group is bound to know the route, and we are all grown up enough not to need a "leader" for each group - teamwork is the key.
The above may not seem practical - lining up in 7 small groups, watching where your mate goes and then quickly changing line (a bit like runaround, for those old enough to know it) and I think many of you would not wish to go that way anyhow ("Sunday is the club ride and it should be a steady, large group social ride"). Trying to accommodate both views will always bring us back to this same issue - it seems to have been raised so many times before and we are still in the same position.
Myself,.. I am quite happy knowing I can turn up and join a group that does exactly what it says on the tin