I put some work into CWV for the next update. This is probably close to the best that can be done given the nature of the type of site.
There's really three things here that prevent this from getting super high on things like GTMetrix etc.
1) We are loading the thumbnails from the source sites, because there's no way to download them fast enough to update potentially thousands of models every x minutes, nor would we be able to set a cache time that both pagespeed would like and would actually be useful (since the thumbs are constantly updated). It's also impossible to size the images correctly, because the sites deliver various sizes.
2) I can't move bootstrap out of the the <head>
<base href="https://gfy.com/" /><!--[if IE]></base><![endif]--> tag without breaking the layout. I can't move other CSS out of <head> without causing layout shift.
3) I cannot reduce the DOM size much, because of the nature of the thumbnail grid display.
IMHO, Pagespeed stuff like this should be taken with a grain of salt. Google would love nothing more then if your site was nothing but times new roman text with basically zero CSS.