The potential issue here is your definition of 'key' and 'much benefit' because if you're using a narrow and specific interpretation, where you expect his passing to win us games or for him to be standout dictating play alone, then there's no point discussing further as we'll be too far apart of a realistic expectation. Or do you think his passing has no meaningful or 'key' effect and we would have achieved the same if it had been Lindelof/Maguire/Varane in his place (or a combination of those two)? You only have to look at the Fa Cup final where Guardiola said himself that Martinez's ability to pass into the middle of the pitch was key to beating them.
Otherwise, I would say a lot of his games in the first season are examples of his quality on the ball which was 'key' as much as anyone one player can have an impact on the team. There are literal passing compilations of just his first 7-8 months with us that some defensive players would be lucky to have over several seasons.