I recently learnt about Shopify's flagship new OS 2.0 functionality and brand new Shopify theme dawn.
I read the blogpost about the supposed speed improvements, but upon checking the speed of the new theme, it only hits 55 page speed. This is for a theme which doesn't even yet have third party addons installed.
The score with that tool doesn't equal speed or performance, it can be used as a guide to try to identify potential performance issues, but the score is largely based on apps used, and some quirks can make the score fluctuate wildly - one recent example: I had a site scoring 88/100. One of the warnings recommended setting a defined height and width of images on the page. This has zero affect on performance, but after implementing that the site scored 100/100.
With any performance tool, use it as a guide but don't sacrifice engaging features or site design just to improve the score (assuming you're on an ecommerce site and your goal is to improve conversion rate).