In Nick Mullens first 5 games as a starter in 2018 he threw for:
262
250
221
414
332
There’s a lot more examples of guys like this. I didn’t look at Jake Browning’s stats last year but he comes to mind as well, along with of course Kyle Allen. Anyone can look good for a few games until the opposing DC gets some tape and starts to actually game plan for whatever attributes stand out on film. Then trash QB reverts back to trash QB and is buried on the bench again.