The only way to judge someone is to work with them closely for months/years.

I disagree here. At some point, you're going to have to delegate and give up in micromanaging this process. There's no way Satya Nadella has worked with each Microsoft VP for years or fills openings just with his intuition.

If mostly every manager Python Pat worked for said they were head and shoulders above their peers and has an executive position in their future, then are you going to just ignore their feedback? Career advancement certainly shouldn't be a matter of being lucky enough to have enough face time with the people who make hiring decisions... I guess at the core of this process is trust, trust that the folks filing the review paperwork are doing so correctly, but if you can't trust your managers, you're problems are larger than a review process.