For reference, another company that sells developer tools, JetBrains, has around 2000 employees.
They have a suite of IDEs supporting a multitude of languages, that are almost universally considered best in class. IDEs are not an easy thing to build. They developed and maintain the Kotlin language which has all but become the standard for Android dev. And they have integrated team collaboration tools that range from project management to CI to cloud dev environments.
Atlassian on the other hand lol.
It is to be determined if "doing an Elon" will work out for Twitter in even the short term. Give Twitter 1-2 years of "doing an Elon" before we judge the success of this approach.
The public UI (and performance) of a SaaS business is the one thing that adds value to society and is valued by its customers. Yes, new products development is a really great place to put some people, but how often do you see those large companies develop something good by themselves?
Most engineers are not in a business to support the day to day running of an app. They're there to build new things to provide growth and support change. This is why you can do an Elon and fire 75% of the staff without something collapsing immediately. That strategy even works in the long term if you're happy to scale back future ambitions and focus on a single app. It wouldn't work for most companies that are constantly fighting for market share though.