So I have the same speed test issues of course... because well all Squarespace sites do (unless maybe dev mode). 7.1 does seem to test better than 7.0.
On tools like Pingdom the actual load times are very satisfactory (1.95s with a score of 88...would like to see a score of 95 or better though). And in the "wild" SQS sites load at a fine speed and in some cases faster than sites that test better. BUT when testing in Lighthouse and GooglePage Speed the results are not awesome.
Squarespace has a great set of tools matched nicely to the needs of many businesses and non-profits. The client/designer collaboration and handoff process is smooth and the system flexible for clients after handoff. I've used Wordpress, Webflow, other WYSWYG editors and Squarespace. Out of all of them Squarespace has produced the best client satisfaction for tool set, ease of use, performance, flexibility and maintenance. But again speed testing represents the platform poorly.
I've researched, what seems endlessly, on how significantly speed tests results impact SERP rank and have found no definitive answer. There are even articles available about why you should ignore speed testing results and just go with actual load times (so maybe speed test results don't matter). What I have found is that Squarespace sites, just like sites built on other platforms, can rank on page one of Google if content and SEO strategy are good.
Handing off or maintaining client projects in other platforms like Webflow is a headache as the flow is awkward but the platform generates great speed testing results. Also AMP which is available in SQS can impact SERP and speed performance and it's hard evaluate how it impacts results...but it should be positive.
But I wish Squarespace would address speed testing and it would feel even better to use Squarespace for projects. And easier to demonstrate the platforms strengths.
as an aside: Website Grader use to be a good tool to use but with Hubspot's changes to it, well performing sites have dropped in scores.
Just leaving this here. https://blog.chromium.org/2020/05/introducing-web-vitals-essential-metrics.html