I think the confusion lies with the fact some are seeing "Holidays" under another section (and not just "Other"), ie. it might appear under iCloud or another subscribed area. Now I could be wrong, but if an Holiday calendar appears elsewhere then it was added by the user and should therefore be able to be removed by said user.
But if for example you added or subscribed to an Holiday calendar on your Mac and it was placed in the iCloud section, although it would be available across all of your devices, removing it might mean doing so from the device it was added (ie. the Mac). I think this was mentioned before, but some time ago Apple had issues with the "in-built" Holiday calendar appearing (under "Other") and the only work around was to subscribe directly, but if the in- built started working again you ended up with two until you removed the user added one!
I believe the issue in this discussion with regards to removal of certain calendars depends on several factors, are they default App in-built (ie. tick box activated), user added on a per device basis, user added and placed under iCloud (so they appear across all devices) and subscribed (either per device or under iCloud), all except the in-built will have a specific way to remove depending on how they were added.
If I've missed anything or got it mixed up I'm sure someone will help correct the above, but that's how I believe the Calendar App functions.