This is sort of like "if you give a mouse a cookie", but ...
If you give Keenum a healthy offensive line, he can be enough of a threat to let the run game work.
If you give Keenum a running attack, he can find a way to create 15 play drives.
If you give Keenum 15 play drives, he can turn a 60 minute game into a 6 possesion game.
If you give Keenum 6 possession game, the defense can expose the flaws in the Steelers, Bengals, Patriots and Lions offenses.
If you expose the flaws in those offenses, the Browns efficiency is enough to win any or all of the next 4 games.
Belicheck and Burrows might cause problems, but even those teams have notable weaknesses that can be exploited.
I think Keenum is capable enough enough to drive Stephanski's meat grinding machine to 4 more victories.
I don't think Keenum becomes a liability until you face the Ravens, because Lamar Jackson is talented enough to force a shootout. Browns chances look much better with a healthy "jitter free" Mayfield against the Ravens.