That's odd. I personally really like the Gutenberg editor for writing (and similar block-based editors like Notion). I have never experienced the lag on a dated 2015 laptop. Out of curiosity, which device you're experiencing the lag on?
I run WP both locally and on a $5/mo Digital Ocean droplet. On Firefox, on a 2014 MBP running Catalina I have no lag issues.
I do find Gutenberg's UX a bit clunky though. But I also recognise that it is the first step to a full WYSIWIG site editor approach that site builder plugins like Divi and Elementor have found success with.
2015 MBP, running Firefox. I've also experienced the lag on Chrome.
Right now I'm transcribing old Irish-language stories and giving a commentary about various features. I notice if the story gets too long, or if I get too many bullets in the list block, it starts to get super laggy. I've noticed it across both browsers. And the sad part is the "long" really isn't that long, about a page of stuff in Pages/Word.
I’ve found that in themes that use WPBakery or ACF for layout is that there is definitely a happy path that involves swapping your text into one of their provided templates and calling it a day.
