[Author here]
> So why is Linux Mint with Cinnamon better than Ubuntu Cinnamon Remix?
There are 3 categories of difference: app selection/packaging, look and feel, & upgrade cycle.
1. Mint removes and blocks snapd and uses a natively DEB-packaged browser and email clients. Me personally, I don't mind snap -- it works well these days -- but some do, irrationally or not. Mint eliminates that problem. It replaces it with Flatpak but disables unverified apps on Flathub, which leaves very little. This castrated Flatpak is much safer, though.
(Zorin doesn't. It offers both, in their full forms.)
2. Packaging extends to the other apps and accessories. Ubuntu Cinnamon only changes the desktop itself to a Windows-like one. Almost all the other components are ordinary GNOME ones. That means no title bars, no menu bars, just hamburger menus, and a phone-like UI.
I strongly dislike that UI, personally. Many do. _Most_ of the Mint components have the traditional Windows-like UI: file manager, text editor, PDF and image viewers, etc. This makes it more familiar and comfortable.
(Zorin does not do this. It offers GNOME-style apps. Its Windows-like desktop is the only Windows-like aspect.)
Mint also uses very dark and muted colour schemes. Many prefer that, especially older users. I find some distros -- almost any with KDE -- actively unpleasant to look at. I dislike Fedora's child-like pastel-hued wallpapers.
Mint also changes and replaces a lot of the accessory apps, bringing related functions together into larger, more function-rich apps: a welcome screen, a backup and system-recovery tool, an update manager which also does release upgrades, and so on. It has a bigger, better app and accessory selection built in, with more traditional UIs.
3. Release cycle.
Only the flagship GNOME Ubuntu has true LTS releases. All the remixes have shorter lifespans. This is not highlighted much but it matters. You don't get 5Y of support on anything except GNOME. Users get confused between interim and LTS releases. I have often encountered people who can't remember that only even-numbered years have LTS releases, or who forget that it's always the earlier release of that year, or accidentally install interim releases and then are trapped in a rapid upgrade cycle.
Mint only does releases based on Ubuntu LTS versions and it supports them for the duration. Point releases are minor and safe. It's a simpler, easier cycle.
## Summary ##
Mint has been around for most of Ubuntu's life. In the early days it just did quieter themes, and bundled restricted codecs and drivers that were optional on Ubuntu. It was a little easier to install and looked tamer. That was all.
Then around 2011 Ubuntu moved away from its GNOME 2 desktop and went its own way, and started introducing innovative tech like Ubuntu Touch, Snap, the Mir display server, etc. This upset a lot of people, and the existence of the official remixes wasn't enough to calm them.
Mint saw a chance. It retained the classic-style desktop, first with GNOME Shell extensions, then a fork, and also stepped up very early to support the Argentinian MATE project that forked and continued GNOME 2.
It positioned itself as the safe, sane, easier choice to the somewhat experimental Ubuntu. Turns out a lot of people wanted that. It's been very successful.
Ubuntu: somewhat experimental, tracks upstream GNOME closely. Remixes have shorter life spans. Snap everywhere, like it or not.
Mint: simpler more traditional desktop _and apps_. Slower release cycle. Safer, neutered Flatpak, no Flatpaks installed by default. Always free.
Zorin: simpler more traditional desktop with attractive light, bright themes -- but only the desktop, not the apps. Excellent desktop-customisation tools. Snap _and_ Flatpak. Has cut-down free versions, but flagship version is paid. This bundles tens of gigabytes of freeware as Flatpaks, so needs more space than any other distro.