Second of all: no, Arch is not as easy to install, specially for someone who is looking at Manjaro as a possibility.
And believe me, I was once a Manjaro user.
And for 99% of Manjaro users, what they really wanted was Arch with an installer. Which is what Endeavour OS is. (Although I’ll never understand why Endeavour people didn’t just develop the tools FOR Arch instead of wrapping it all up as their own).