I just noticed that WP Rocket does the same. Testing a website this afternoon, and viewing the source code, yielded 28 .js files. Using WP Rocket and testing with GTmetrix, yielded only one .js file, a lazyload.min.js script. The results in GTmetrix were obviously 99-100%.

I find this misleading, again, as the website is not as fast for me, as a user, than it is for GTmetrix.

As a developer, I would try to bring those 28 scripts down to a maximum of 5-6 and be able to test the impact.