I think you're right about the stadium. If ADUG had decided, for example, that Everton represented a better long-term bet for their investment, I doubt that Mansour would have been swayed by the fact that City had a more or less new stadium at the time while Everton would have needed to build one as a matter of priority. As it was, City ticked more boxes than Everton even disregarding the issue of them needing a new ground.
The fact that there was land available for development around City's stadium, both within the framework of the club's requirements and outside it with the opportunity for nearby housing development, was definitely regarded as a plus. However, that was very much a bonus rather than a requirement of ADUG's for a deal to be done. They hadn't foreseen it when formulating their original intentions.
I know that money was no object in terms of the plans they were putting together in the early days. The original intention was to spend big on the collar site to attract partners and have a significant destination, as described in public documents from 2009 onwards, up and running a decade or more before now. Unfortunately, that was nixed by political changes in the UAE circa 2012, when it was decided that what might be regarded as vanity projects abroad weren't in the interests of Emiratis and overseas projects implemented using UAE funds should operate on a commercial basis.
Through the days of economic uncertainty caused by austerity, Brexit, Covid and war, no partner came forward with realistic proposals for a venture on land adjacent to the ground until Oak View advanced the idea for what would become Co-Op Live. Under the plans being advanced at the outset, where there'd have been significantly more largesse from ADUG and attracting major partners thus probably wouldn't have been much of a problem.
The political requirement from the UAE for this investment to be seen to offer value in commercial terms is also the reason that a lot of people find the architecture in ADUG projects rather underwhelming. They were at first prepared to contemplate building a new stadium at whatever cost it took to ensure that it was considered breathtaking. This consideration no longer applies to the developments we're now seeing.