Building a new roster where all the free agents are dumbed down a bit is probably the best workaround for this year.
Also bear in mind how the AI gets to its OVR rating for its scheme. In the case of Phillip Dorsett - his Size, Durability, and Intangible sub-grades are all low relative to other players on his team. I don't think you can change his height / weight, so you're stuck on the Size grade, but the Durability grade ought to be easy to raise by increasing INJ / TGH (most of the rookies have low ratings in these two categories this year). Raising those two alone may be enough to get the AI to keep him. If it's not, then raise the Intangible grades the Colts AI GM values (I think they value Route Runner WRs, so RRT would be the most useful rating to increase).