They're overrated today because they were good at some time in the past and people have to catch up. As for why they're not that good right now:

Elementary OS had at some point in time perhaps the most polished and accessible user interface out of any distro out there. This was mostly due to how much time and effort they had put into their in-house Pantheon desktop environment. And if they would have continued their efforts, then it would have continued to flourish. Unfortunately it failed at keeping their momentum, this is most likely related to internal disputes. I say this because over the years a lot of important members from their team have departed. Right now; it's just a shadow of what it once used to be and the likes of GNOME, KDE and Cinnamon have far surpassed their Pantheon.

While Elementary OS is just plain bad at this point, by contrast Manjaro is actually not that bad. Arguably, it does a lot of good things; Btrfs+Timeshift being one of the big ones. However, freezing packages in a rolling release doesn't make any sense. Furthermore, it's just very unprofessional to let the SSL certificates expire. Mind you; it didn't happen just once or twice, but four times?!?! Today, if one wants a stable rolling release that holds their hands, they should use openSUSE Tumbleweed. If they want to use Arch, then they should just use Arch; archinstall exists. And if one is not able to install Arch using archinstall, then they should question themselves if Arch is even the right distro for them. Finally, if they seek any kind of hand-holding, then there's a plethora of derivative distros of Arch that are as good, if not better than Manjaro. So just to make myself very clear; Manjaro is not bad, it's just overrated; people gravitate too much towards it based on old videos/articles and what not, but it doesn't deserve that gravitation in its current state.