I'm not sure what you mean. Saints Row 4's large criticism was that it was too different from SR's heritage what with being a super hero game instead of GTA on crack. Past that Gat out of Hell isn't a mainline title and was even further out there, and then Agents of Mayhem wasn't even a Saints game, and I enjoyed the hell out of that game's unique merits.

The SR reboot was the first real Saints Row release since 3, so you could say that it didn't do enough different (which I can't speak for, I didn't play it), but saying the series hasn't done anything new since 3 is not correct. Whether those games were super great or not is a different discussion, but they were doing something different, unless you just didn't specify between something different for the series or something different from all other video games.