Mac Jones is a pretty good QB IF PLAYED IN AN OFFENSE TAILORED TO HIS STYLE. Many evaluators have deemed him a finished product but the NFL is a different animal than the NCAA. He does have his weaknesses. He will often rush his throws under quick pressure, something he got away with in college but you would be concerned in the NFL. He will at times trust his arm too much. Again something he can do in college but won't translate. He seems reluctant to extend plays and many evaluators see him as going down too easily when pressured.
Like all rookies, he will take some time to acclimate to the NFL. That's why SF would start Jimmy G at least this year and redshirt any QB they take. If they take another QB Jimmy could potentially finish his last 2 years of his contract in SF. The bottom line taking Jones probably makes sense. He will have a decent o-line in front of him, a strong run game, and decent receiving corps.
So as a Ram fan if SF takes Jones, the earliest we would see him would be in 2022. He's a pocket passer who is not known as a scrambling threat. Even if he's coached up to move, i.e. rollouts, etc., he's no Murray or Wilson. That said he can be the kind of QB the Niners are looking for. If he reminds me of anyone it might be Brees when he came out of college due to his stature and how some evaluators think his arm strength could be better. Well, the same was said about Brees but he proved that arm strength is something that can be improved with the proper strengthening and training regime. Eventually, he could be a very dangerous opponent.
Three years from now IMO he would be a bigger threat than Murray. Why? Because he reads defenses far better than Murray, and he protects himself. My opinion of running QBs is bearing out as they begin to get hurt and then the offense designed for their skills fails just like AZ did this year. There is no way to back up a running QB like Murray, Mahomes, or Jackson. That's why a pocket passer like Jones might keep SF dangerous for a long time. IMO SF will be the main divisional competition after this year unless Seattle gets their act together.