I don’t know if this will help you, but I thought I could share some personal observations.
I have a couple of MacBooks, and a few desktops. Not experiencing issues on any of them when designing for hours in Webflow.
Even my old war horse (MacBook Pro: 2013) makes the journey with no issues. I will say this, every machine I have has AT LEAST 16GB and SSD storage. I do use security software, but when in the design mode real time scanning is off.
The behavior you are having is very suspect. I would first isolate the browser, then background processes running on your machine. Take a look at CPU and memory usage.
I personally use Chrome Canary with zero extensions installed for Webflow work. Leaves me with a clean browser for that task. I am in the boonies but have a GB connection to the net, and no latency issues. DNS provided by Cloudflare.
Wish I could be more helpful.