Large-scale layoffs very rarely (i.e. never) simply cut people that are "bad at [their jobs]."
I've also seen cases (and this appears more relevant in ARM's case) where the company just hired way too fast. It wasn't that people who were laid off were necessarily bad, but there were just way too many people for the amount of work, and so in absence of clear purpose a lot of people would have tons of "make work" meetings that were really there just so they didn't feel totally useless.
I'm certainly not saying all layoffs are like this, but I do take issue with the idea that layoffs never have a net positive effect on culture.
Regardless of if you are "[hiring] way too fast" or "finally [getting] rid of subpar performers," layoffs are still, by definition, firing a bunch of people's coworkers. Simple work efficiency, which is what you'd theoretically be improving in both of your examples, has relatively little to do with company culture, so your examples aren't very compelling evidence.
Neither points to a very healthy culture to start with.
I've been a few times and I recall losing lots of friends and valuable team members. Even management typically doesn't spread the ridiculous myth that they're laying off people "who doesn't want to do their job and/or is bad at it".
Layoffs are heart-breaking and I can't earnestly believe that someone who has been through them would have this "counter-take".
Theres more than one way to skin a cat as they say, so layoffs can be seen in a few different lights.
Edit. Just because a company is listed on the stock market, like govt's doesnt mean they are not fronts for criminal activity!