Not the first time I hear of this, but I thought it was a blink-specific issue when using severely nested structures (e.g., html pages written using visual editors like Elementor or Webflow)?

For quite a while, I had to keep using flexbox instead of grids, because grids killed performance, funnily enough. That seems to have been rectified with modern browsers though, funnily enough.

Flexbox is great and having nested flexboxes is also great. It makes building responsive pages a bliss. Learn it if you are having trouble with it, it is really not that difficult. Grids are much more error prone and allow for much less flexibility.

Useful insight: any sources?