Wasn't there a hubbub a year or so ago about a pro using an integrated motor that hid in the downtube?
Anyway, my feeling is if you don't have the power in your own legs to hang with the A group, you just don't belong there and need to ride the B group. B group riding is fun too.
But not everybody feels like you. I don't. Not all A group rides are the same. B group rides for me are a bit boring and I am no longer young. But some A group rides turn into flesh eating contests.
That's where having a bit of assistance may help. Hey it may turn into a Harley thing. Guys on $15K e-roadbikes pacelining at 30 mph whenever they want...will need a motor to keep up.