Endeavour is essentially just a GUI installer that spits out a proper Arch install with a few nice-to-haves pre-installed (like yay for example), and some good defaults (like increased parallel downloads for pacman).

Manjaro, on the other hand, holds back packages from the main Arch repos for testing. Which is reasonable in theory, but it means you can have compatibility errors if you install things from the AUR (which is the main draw of Arch IMO).

The Manjaro team has also forgotten to renew their SSL certificates multiple times (and told people to roll back their system clocks to fix the problems it caused), as well as DDOSing the AUR a few times too.