Sounds like some bad software or something extra CPU intensive then. I use R5 2600 on W11 and it can handle everything I need with ease like web browsing (depending on pages and tab count it can be quite demanding), at least 3 VMs at the same time (2 Windows, 1 Linux), gaming, video transcoding. All that is not happening at the same time, but I can’t remember last time I checked Task Manager to see what is using my CPU.
I thought the comment was for R5 1600 which is close to my R5 2600 and those Intels were close in performance. Checked specs of them and I see they are not, also thought that i5 6600K was 4/8. In this case, yeah, upgrade probably was more than noticeable.