I've taken the cyclocross bike on the group ride twice recently. No issues.
It's a touch heavier, touch slower steering, 28mm or 30mm Gators (can't recall), canti brakes, 1x with suboptimal road gear range (40t and 11-28)...........etc.....
I can understand the "cost" difference in wattage between two bikes mattering.........if spending a good time right at threshold. At threshold power yeah, 20w matters. If not, 20w ain't gonna matter in a one minute 600 watt hill sprint or a 400ish watt few minute hill climb. The ratio of output to loss is just not important for a group ride. (Yes, according to math, it matters, but you probably won't succeed in a hill breakaway because of it).
You've either got enough power for that kind of attack or move, or you don't. Or you're too fat all-together.