I would say smartphones and tablets are new devices, not, per se, PCs.
Smartphones did bring something huge to the table, and exploded accordingly. But here we are, less than 2 decades from their introduction and... the pace of improvement has gone back to being incremental at best.
They're, at a minimum, PC replacements in the sense that I'm currently on the Internet and posting on a message board from my bathtub instead of needing to go over to my desk to do that.
Smartphones did bring something huge to the table, and exploded accordingly. But here we are, less than 2 decades from their introduction and... the pace of improvement has gone back to being incremental at best.