[cflsystems]

I don't think it is a good idea to not use aggregation. XC5 has tons of css/js files so even if you do not see some page speed difference think of it as
- loading 100 files vs loading 1 file

As for the Lighthouse project regarding css/js - while XC5 loads some css/js files based on page being shown there is still tons of css/js that load based on module. So if Module A loads css/js files only because it is active they will be included regardless the page and of course if it is not Module A page will be reported as "unused". But you cannot do anything about it unless rewriting the module...
Oversized images will be reported almost all the time as XC5 loads image and shrinks it due to improper css - product images, category images, etc. The image container has a border and if you set image size to 200px for example (in admin) the image being loaded is 200px, its container is 200px but usable space is 196px (depending on border width) - image is shrinked down to 196px....