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This is not special to Meta in any way, I observed it in any team which has more than 1 strong senior engineer.
For what it's worth, 20 years ago all programming newsgroups were like this. I grew my thick skin on alt.lang.perl lol
Of course technical discussions happen all the time at companies between competent people. But you don't do that in public, nor is this a technical debate: "I don't recall talking to you about it" - "I do, I did xyz then you ignored me" - "<changes subject>"
Always good to talk face to face if you're have strong feelings about something. When I said "talk" I meant literally face to face.
Spending a decade or so on lkml, everyone develops a thick skin. But mix it with the corporate environment, Facebook 2011, being an ex-employee adds more to the drama.
Having read through the comments here, I'm still of the opinion that any HW changes had a secondary effect and the primary contributor was a change in how HHVM/jemalloc interacted with MADV.
One more suggestion: evaluate more than one app and company wide profiling data to make such decisions.
One of the challenges in doing so is the large contingent of people who don't have an understanding of CPU uarch/counters and yet have a negative opinion of their usefulness to make decisions like this.
So the only tool you have left with is to run large scale rack level tests in a close to prod env, which has its own set of problems and benefits.
That said, one of the comments above suggests that the HW change was a switch to Ivy Bridge, when zeroing memory became cheaper, which is a bit unexpected (to me). So you might be more right when you say that the improvement was the result of memory allocation patterns and jemalloc.