I personally wouldn't appreciate them doing it as Colapinto is straight-up garbage. I would appreciate them fixing his driver rating though as he starts in the late 70's when I start a career and he is a 67 at best. No idea where you get the idea he has huge potential unless it's a huge potential to be mediocre for years (as a fair few drivers have achieved that over the years and kept their place on the grid).
Replacing Jack with Colapinto also takes out an additional driver from the available pool of drivers and that's already pretty sparse. If they just put Doohan in the available-to-sign drivers then that would be fine, but it would be a departure from what they normally do as he wasn't in F2 last year.
That being said, while Franco is only classed as a temporary driver (hence the reason for the replacement not already happening), I fully expect him to complete the real-life season as if you can stink up the joint this badly all year and still keep your seat then you're basically a permanent driver. Therefore it would be more realistic for him to be the second driver, despite the fact he's absolutely honking.