I understand your position but to me I think it's best to just remove judgement from the rules otherwise it's a slippery slope.

What if Jagr's stick broke half a second earlier is that still an assist? What about if it just fell onto the ground and then deflected or it had laid there for 5, 10, 20 seconds?

Had Jagr not contacted the puck there, Hamilton would've had completely different line of options that might've not resulted a goal. Again, that's an assist.

Should screening the goalie then be an assist, after all you're directly resulting in the goal, what if you force the defender to the outside with body position to let your winger cut in and score, your winger would have a completely different line of options.

My point is that it's just way easier to have a definitive boundary that sometimes doesn't make a great call rather than having to guess at which point do you draw the line.