“software-properties is an old gtk application essentially focused on deb/apt world. Many of its features are dangerous or too complex for normal users (removing main, enabling proposed, source without specifying what, …)”
First it was Mir, the alternative to X and Wayland. Then it was Unity (notice the name!), yet another desktop environment. Now it's snaps, as an alternative to flatpak.
Are you noticing the pattern? It's always Canonical trying to force some distro-agnostic tool into the Linux community, so other distros start depending on Canonical. Always doing this through unnecessary fragmentation.
To be clear, fragmentation is not always bad. Sometimes it enables people to appease different target demographics; specially in the context of Unity. However the way Canonical does this stinks "we want control!" from a distance.
With that in mind, look at the part I've emphasised. It shows the actual reason why Canonical is ditching software-properties from the defaults: because it wants to press further for snaps, in detriment of .deb packages.
What follows is basically an excuse. I don't think it's actually removing it because "it's too dangerous" or whatnot. However, if anything "this is an excuse, not the real reason" only adds injury, because it shows 1) that Canonical sees no problem misleading the users on why it does something; and 2) the people working there are so detached, but so detached from the userbase that they don't get why this would rub users the wrong way. (It's basically a "you're trash too stupid to not cause itself harm" dammit.)
Ah, by the way: Canonical was always some sort of Apple wannabe.