Also I don't like the place of the button on the G27 for the Ebrake, not really practical.
OP just watch the 1 hour long Drift Bible on youtube and you'll see e-brake have it's own purpose in drifting
Anyone who actually understands drifting should be able to drift just fine in a bone stock car. They probably won't be linking entire tracks, but they should still be able to make a decent showing.
Handbrake very much boils down to personal preference. I don't like using it in general (and it's awkward for me to use on my DFGT, so that works out), but some people use it all the time. I'll tap it occasionally for a little clutch kick, but that's usually to correct a poor entry.