I think OP is using these less as staging and more as dev environments for individual developers. That seems like a great use of a single server to me.
I'd still like a staging + prod, but keeping the dev environments on a separate beefy server seems smart.
I've been using a development server for about 9 years and the best thing I ever did was move to a machine with a low-power Xeon D for a time. It made development painful enough that I quickly fixed the performance issues I was able to overlook on more powerful hardware. I recommend it, even just as an exercise.
For similar reasons, in the Google office I worked in you had the option to connect to a really intentionally crappy wifi that was simulating a 2G connection.
The "platform" software runs on is just other software. If your prod environment is managed kubernetes then you don't lose much if your staging environment is self-hosted kubernetes.
Load balancers, IAM roles, kubernetes upgrades, postgres upgrades, security settings, DNS records, http routes... there's a lot that can go wrong and makes it useful to have a staging environment.
