I noticed that Lighthouse has drastically reduced its scores even for some of the fastest sites I’ve ever built. Where they used to score 90, now they score 1/3 of that with no discernable change to the site itself. I think Google has changed how they calculate the scores, to be honest. And it stinks because the clients who know about these testing tools want answers I can’t give them.
For the external script things that Google recommends you make changes to, I feel your pain. I don’t know whether Google realizes that not every site is built using plain static HTML, lovingly hand-coded by artisans who do nothing but write the most basic of code. A ton of us use CMSes where it would be a real pain to fork them just to cater to the whims of a page speed score.
That said, I did get wind of a couple of plugins that are supposed to help with this. They’re pretty new and I didn’t have 100% success with them on my sites (which rely heavily on page builders) but they may work for yours. Here are the links to them:
https://wordpress.org/plugins/host-everything-local/ - Host Everything LocaL (HELL) does what it says on the tin: It grabs a copy of whatever external scripts it detects and drops it into a directory in your wp-content/uploads so it resides on your server. My problem with it was that it didn’t detect enough scripts, especially Google’s own bloated Analytics and GTM JS code. For that you’ll want a plugin called CAOS (https://wordpress.org/plugins/host-analyticsjs-local/). But HELL does have some pretty neat preload and prefetch options that may help you.
For fonts, try Optimize My Google Fonts (https://wordpress.org/plugins/host-webfonts-local/). Again, does what it says by hosting all web-based fonts locally. I couldn’t tell how much it was helping me but every site is different. If that doesn’t work, try Elegant Custom Fonts (https://wordpress.org/plugins/elegant-custom-fonts/). I’m using that on an Oxygen Builder site, by Oxygen’s recommendation.
In general, it feels like Pantheon’s slowing down a bit overall. I can’t get near the speeds I used to get from Pantheon in the past. It seems to have degraded since December for some reason. And especially if you’re using any kind of page builder or any plugin that defeats Varnish caching. I’ve been several rounds of this with Support at both Elegant Themes and Pantheon and each points to the other as the culprit. I’m hoping that theme builder vendors and Pantheon can work together more closely, with Pantheon providing some kind of developer testing account so that the incorrect assumptions the plugin/theme developers make about how “all hosts do things” can be mitigated. If Pantheon does something like that, I can only see faster, more secure plugins and themes in our future.