Twitter's failures are solely due to Musk's changes in corporate governance (e.g. boosting fringe right-wing content causing its existing userbase and advertisers to flee the platform), not due to any engineering problems caused by reducing headcount. Strictly from an engineering standpoint, Twitter works just as well as it did before Musk took it over.

As I wrote in another post, if Musk had never purchased Twitter and Jack Dorsey performed the same reduction in engineering staff, I doubt the site would be materially different from how it was pre-Musk.