At the scale of O365 it totally makes sense to look at a high performance non-GC language for your core systems that see the most traffic (I say this as a .Net dev).
Too bad you have to be in the office 50% of time for that role.
That surprises me since I'd expect that you could get really far with hot path optimisation.
Not sure microsoft’s problem is the language. Their frontend JavaScript code is bloated and slow. It makes office365 feel slow and there are so many bugs in the azure management tools. I assume the backend code has the same low quality.
I imagine the goal here is to optimize MS' compute and hosting costs. The core pieces of O365 probably handle many billions of requests per day. At that scale even small optimizations can be worth millions a year in cost savings.
Sounds like a skill issue to me. Their code sucks and they want to blame the language.