Distrowatch is a popularity contest based on clicks on the DW site. Pretty meaningless (but not completely) if you ask me. I do think that MX Linux has gained users faster than any other distro in the past year(s).
If we want more meaningful popularity numbers let's look at forum activity. I think we have two leaders. Linux Mint forum and Ubuntu forum (+ official flavors like Ubuntu MATE and Kubuntu forums).
I don't have numbers for the latter, but Linux Mint forum states:
Most users ever online was 2029 on Mon Apr 08, 2019 9:27 am
The same number for MX Linux is:
Most users ever online was 717 on Tue Oct 30, 2018 5:46 pm
In terms of popularity I would put Linux Mint first (because we have an actual number) and Ubuntu (+official flavors) second. MX Linux seems to have more forum activity than Manjaro and if we add antiX the gap becomes even wider. So I would say MX Linux is the third most popular distro in the world based on forum activity, which is a much better measurement than Distrowatch IMO.
Of course forum activity could be analyzed in much more detail. Before someone says that MX Linux has less forum activity because it has less bugs, that's not how it works. A popular distro with a bad release will see a short burst of forum activity with problem/bug reports. But Linux users aren't loyal. And after that short burst of forum activity users start leaving and forum activity goes down to a level much lower than before the bad release happened. So you can't really fake forum activity by buggy releases. Users just leave instead one by one.
This is what happened to Ubuntu and official flavors and the reason the Ubuntu community is (relatively) smaller now than 10 years ago.
That being said I don't think any other distro deserves the top spot on Distrowatch better than MX Linux. That's some crazy dedication from a small team of very helpful people. It's almost like I feel like a bad person when I see how much help they give for free despite being busy with software development, website, forum, documentation etc.
So I see the MX Linux DW ranking as a reflection of all the hard work the MX team put in, not only writing better software, but also being more helpful.
I just don't want the DW ranking to be confused with the most popular distro (in terms of users). In fact, since MX Linux is still relatively "unknown", there is a chance that the DW clicks will keep coming and MX Linux can stay on top for some time. Just like Linux Mint, MX Linux can also continue to expand its userbase long after it has peaked and fallen on Distrowatch.
Note to self and others: SysVinit is a good option. However if you run into problems try with systemd first. This applies to AppImages, Flatpaks, GitHub packages and even some Debian packages.