Love Greta and agree: their last album is just epic!Greta Van Fleet, as much as I hated them at first, just delivered an epic rock album that matches (and exceeds as a complete work) many of the bands albums they are compared to - I was shocked how good it was… it’s serious/powerful but still positive/clean and weighty (yes, it can be done) so reviving a sound/era is good if your committed to it
Said that, I don't think they are aiming for an specific era (try not to think about the clothes, I know it is hard). Not as declared as JM is with that song.
Listen to "Broken Bells" and tell me it isn't an original tune. Man, it's brilliant!
As for JM I'll reserve my thoughts to after I hear the hole album. The single is never his best music of the album, IMHO. But he has aways some amazing ones that just shine over the roof. Like "Walt Grace Submarine Test".