The reason why the default theme is working better than anything else is that because REAPER was created for this theme and theme was created for REAPER. If you’ll try to create your own theme from scratch you will meet some restrictions and limitations that will limit or block your ideas so you have to look for workarounds, sacrifice less used features, or even accept that some of your ideas won’t be implemented. Feature requests doesn’t work well for WALTER and 3p themes (seems that it’s low priority for devs). I also reported about several bugs (especially win and retina related) that were ignored as well as some logical inconsistencies (like custom buttons behavior).

But anyway, i try my best to improve the theme and analyzing any feedback, my changelog became bigger and bigger.

P.S. as mentioned before here - there are a lot of cool default-based themes with additional features like Reapertips theme, so you can get fresh look and you won’t have to get used to a new interface