That really isn’t true, especially when your system repeatedly fills up RAM and thus slows down your system by saving to disk. Many apps leak RAM too and it’s easier to clean up RAM than quit and relaunch. I have 40Gb RAM and usually have a few dozen tabs open - using an extension that “sleeps” tabs not visited after x minutes recoups RAM in Brave, but Safari can still suck up ridiculous amounts.
Edit: I recently wrote about this (with screenshots) here.