I"m normally near the pointy end of the B group and my strategy is always to hang with the lead group as long as possible. I at least try to keep from getting dropped while another B is still in the group. If I get to the point that I’m getting close to blowing up, my strategy shifts into finding the right time to drop (much better to get dropped with a couple other guys vs. riding solo in the gap). If you’ve hung on long enough or get in a decent second group, the other groups behind are unlikely to catch. I’m usually 3.6.- 3.8 w/kg for the race and that’s usuallly enough to be in the top 5 for B’s and sometimes on the podium.
That’s for actual races, not tour de zwift and other “rides” with hundreds of people. While there are certainly people treating those rides as races, it’s a very different dynamic compared to actual races. As much as people talk about cheating on Zwift, I just don’t see much cheating in A and B racing for actual races. Zwift Power does a nice job and the racing community keeps things in check.