Also seeing this. We migrated our app from web appbuilder to experience builder this past year, and my users do not like it due to performance issues. Experience builder uses way more RAM and CPU, you can watch it on your task manager.
Users complain when using the WAB version their computers remain relatively silent, but when you pull up the experience builder version, the fans start running like crazy. Some users with less powerful PCs state that the new version crashes.
I was hoping these issues would be resolved the closer we got to the depreciation of WAB, but with each new update, it doesn't seem like performance is something the team is focused on. I will have to continue to maintain both applications for this reason into the future.