I only use EndeavourOS and don't speak by experience for CachyOS. While EndevaourOS is a more traditional Archlinux with some additional tools and GUI elements, and some branding, Cachy is a more optimized OS trying to squeezing out performance. I feel like EndeavourOS is a bit more minimal, bit more CLI oriented and is closer to original Archlinux. CachyOS is a bit more opinionated, has strong focus on performance optimizations and may come with a bit more pre-selected applications for a head start. At least this is my impression I get.
I game a lot on my EndeavourOS and its well suited for that case. On the other side, CachyOS will may have an edge on this point and is also well suited for everyday tasks.
Lot of people will recommend Cachy, because of the performance optimizations they do. These are metrics you can compare directly with benchmarks and "proof it scientifically". However all the other differences are not that scientific to put into words and often are a taste and philosophy difference. Therefore I can't say which one is better (even if I tested Cachy too). They just have different focus, building on the same foundation.
