$100B company, maybe they can afford to put some people onto solving this for the open software community (and put the solution into the open), especially since nobody else in the community seems to have this problem.
If you proposed a good solution I'm sure they'd be happy to provide time and money and open source the result. But most of the responses aren't even that there is a solution - they say to split the repository into smaller pieces and spend time and money internally having their internal developers deal with that.
A good solution will benefit everyone who uses git. Codebases get larger over time. There is more forking and experimentation. More spoken languages can be supported. More computer languages can be interfaced. The O(n) operations becoming less than that will benefit you in the future as your code grows.
