He took a step forward mid-season this year. With a healthy offseason to train, they should see if he can take another step forward. Sure, bring in "competition" for him, but it should be someone like Mariotta, someone he can beat out. Enough to keep the fire lit under his rear by that mid-season benching lit and burning.
Punting on him at this stage seems idiotic for the Colts.
Did he? He had a nice game against the Jets in week 11 when he came back, but then he went right back to being extremely inaccurate (3 straight games not topping 50% completions) and more INT's than TDs. He was more effective as a rusher after coming back, but his step forward, was more from horrible to just bad.
The thing is the competition will likely be higher than Mariota just because the supply is bigger than the demand. Although honestly, Mariota is probably better too. Its REALLY hard to complete under 50% of passes, and REALLY hard to have a passer rating in the 60s. His completion percentage was 10% lower than any other QB who had started at least 3 games, and that was Spencer Rattler. His passer rating was 9 points lower than any other QB (again Rattler) and that's not even getting into his 9 fumbles, which on a per play basis only Cooper Rush and Spencer Rattler fumbled more.
ETA: The only guys since 2000 who had lower completion percentages are Akili Smith, Mike McMahon, Tim Tebow, Ryan Leaf and JaMarcus Russell.