What SaaS stack? The backend and frontend are just doing their job, so they're about as heavy as they would be if it was, let's say, an electron app, and the only other services are minio (a glorified web server) and Postgres, which a "normal" app would probably replace with sqlite and save a hundred or two megabytes of RAM. Hell, I wouldn't be surprised if using Postgres was more resource efficient than having your engineers come up with a custom ad-hoc datastore.

All in all, the overhead would probably be equal to two tabs in Chrome.

And calling it a "small graphics tool" is just nonsense. If you're doing UI/UX design, this is THE thing you spend your time in. It's like Premiere for a video editor or AutoCAD for an engineer. If it takes 30 seconds to load and eats half your system memory, who cares, it's what you bought the computer for.

Besides a specific subset of programmers that only use Vim or Emacs, every other professional is used to giving whatever tool they're using to do their job all the resources their computer has. You don't see video editors complaining Davinci Resolve runs a whole PostgreSQL instance in the background.