The man performed very well in 2016, and if we had any semblance of a defense, that should have easily been a 10+ win season.
I'd argue that he stepped his game up even more that year, since we lost one of our best receivers (Torii Hunter Jr), and that he was forced to share time with Malik Zaire. Also, going from Will Fuller as your WR1, to Equanimeous St. Brown was a significant drop. Don't get me wrong, St. Brown still had a fine year, coming close to 1000 yards, but as a true sophomore, he had some room for improvement. I still wonder how much better that 2017 season would have been, had Kizer stayed, since St. Brown wouldn't have had his neck almost broken several times.
With regards to his terrible pro career...
I can't fault Deshone Kizer for getting drafted by a truly putrid Cleveland Browns team. That franchise has been a graveyard for many a promising quarterback. Brady Quinn had a similar experience there, that by the time he was starting, they had already traded away their best players.
Frankly, I'm surprised that Baker Mayfield managed to put up some decent numbers during his time with that franchise.