I haven't used Puppeteer but have seen similar issues with Selenium and Firefox. Yeah you have to code delays for pages to load, use onload events, maybe scan the page for text you expect to see, etc. If this is for your own site (I mean where you're working) you can probably do most QA functions by having some special flags that disable the overlays and stuff. Also if you have disk space to burn, instead of screen shots, you can connect the browser frame buffer to ffmpeg and capture video. That can be useful for QA, since if something goes wrong, you can see an actual movie of what was happening.

Yes browsers eat ram, you just have to deal with that.