I can see how they would be good sprinters but good for the long haul flat terrain or hills it seems like they would die out from having to pull around all that bulk. Though I don't really do group riding so it's really just conjecture on my part.
You are talking about fat guys. There is a big difference. The extra weight is only figured in when gravity is involved.(and it works both ways) Take me for instance. I am 5'8" and 205lbs.(yes I have about 20lb extra hanging on) On a hill I get dropped by grannies on beach cruisers. But in the flats no gravity. Only frontal area and drag and that extra 60lbs of muscle(power) more than makes up for the slightly increased body frontal area drag/resistance. When(optimistic) I get the 20lbs back off I will be able to accelerate and climb a little better but that is about it because my frontal area drag will be about the same.
To illustrate it more, we go on a ride together. You drop me bad on the climbs, but I blow by in the flats. Then you clone yourself and get yourself a tandem. Your clone gets on behind you and we ride again. Now you've got 280lbs on your bike. However, you are reaching speeds you only dreamed of in the flats. Your tandem is cruising along at 25mph and you aren't even trying hard! You blow by me and scream, "Feeeel My Awesome Power!" Then we hit a big climb, you are reduced to a snail's pace and I pull even quickly. I look over and say, "gravity is a b**** isn't it?" Then the climb gets worse and (in reality) this is what happens next. All 3 of us have to dismount and walk the bikes to the top of the hill because we can't climb for ****!
On a side note, I am a native Texan myself. San Marcos is a beautiful place! If you are a youngster, you cannot imagine how much good ol' George Strait helped young men score with the ladies back in the day.