Um, no it is not more impactful. The fact that the fg at the end is a "decider" is a result of all the other plays in the game. A game is won amd lost on the sum of all plays in a game. Every play is important. Early plays dictate late plays. It's all interconnected. Three points earlier affects the need for 3 points later. The impact is not greater at the end than the beginning, it is merely closer to the final result.
With due respect, you are simply wrong in the particular scenario I provided. It's no simpler than can you say with 100% certainty after the game is over that either play
by itself changed the outcome of the game? The answer is unequivocally
yes in the case of the end-of-game field goal miss and only
possibly in the case of the initial drive miss. The only way to change the
possibly to an unequivocal
yes is if you could say every play thereafter would be exactly the same with exactly the same result regardless of result of that initial drive FG. Any reasonably intelligent person, which you appear to be, would have to agree that would not be the case.
In the case of the original debate, that the bobbled snap and inability to kick the field goal, it cannot be stated unequivocally that play altered the outcome of the game. Even if that field goal is made, Seattle still gets the ball at the 20 at worst case and the defense still has to stop them. But it is just as unequivocal that it had a greater impact because of when it occurred which limited the # of potential plays remaining in which to overcome that one play.