Imagine if Stop Drop & Roll was released as a Green Day album and Foxboro Hot Tubs never happened. It would be the highly anticipated follow up to American Idiot, but what would the reaction be? I can imagine that Mother Mary would become a massive radio hit and the album would chart highly initially as it's the follow up to such a successful album, but I think it would be regarded as disappointing. The straight up rock'n'roll sound is such a radical departure from American Idiot. I think fans would like it, but it wouldn't be anywhere near the commercial success of American Idiot or 21st Century Breakdown.
What do you think the reaction would be if it was released as Green Day? Not as harsh as if Money Money 2020 was released as Green Day.
Instead it was released as a side-project under the name Foxboro Hot Tubs and it's a cult hit with the fans. 21st Century Breakdown was the true follow-up to American Idiot and rightfully so, it progressed from that album perfectly and served fans better than SD&R would have done.