I understand, but all I can say is that I had no problem feeling what the writers wanted me to feel during any of the scenes with Jackie.
- conversations between him and V were written convincingly enough to convey close friendship
- he's probably the only decent person we meet in Act 1
- I hate bringing up FPP here, but I kinda have to: watching his face from close distance as life slips away from him makes the scene much more impactful
I don't think anything that happens in Act 2 require more Jackie to work. It's not dealing with V grieving over his death, being traumatized, etc... This isn't ME3 situation with Shepard and kid from Vancouver.
As for the rest, you said that nothing could convince that the story is not drastically altered, so there's nothing for me to add.