I'll say it again, first off all Ambassadors are not created equally. It took my 4th one, and yes I pushed for the changes, to find one that delivered on what I think the promise is.
As such I've learned a few things about how the, at least former, system worked for SNA. If you put in for a SNA it's all automated at that point. Your Ambassador has zero influence over the fulfillment of a SNA. In fact it prevents the Ambassador from negotiating with the hotel on getting you any kind of suite. I've had my Ambassador tell me not to use them since she knew the property and could likely get us into a suite.
It's probably not as black and white as this, but I've found if my SNA doesn't clear 5 nights ahead, they won't clear at all. Just remember only getting 10 per year we only have limited data points unless you are using the one or two at a time, which to me is a waste as I want at least a 5 night block (which also make them harder to clear).
Another point, I was Plat Prem for nearly 10 years, that program was useless as they had no real defined benefits, which is why I dropped Marriott and went to SPG to get an Ambassador. So I was not happy about Marriott acquiring SPG, IMO, Hyatt was the match as their top level matched best with SPG.
I'm betting Marriott gritted their teeth when they decided to keep the Ambassador program. All I know is that mine, who I have an excellent relationship with, is not over worked and is sending me email responses outside her normal work hours. My prediction is the program will be diluted at some point.