Sony didn't push TASM3 back 2 years in order to re-evaluate the series because of numerous complaints about TASM2 just to turn around and film TASM3 & TASM4 back to back. They would be insane to do that given how much the series is struggling as is.
Plus, didn't Webb say he was done after TASM3? How are they supposed to get a whole new crew lined up to do TASM4 back to back with Webb's TASM3? Unless, of course, they just fire Webb now.