To be fair, and this is coming from someone who hasn't seen anything substantial of S5 (accidental spoilers notwithstanding), MLP:FiM does borrow liberally from its source materials, and so do other shows. It's the shared heritage that's showing, I guess.
The Tree of Harmony looks and feels a lot like World Tree from World of Warcraft, for example, and they both take after Yggdrasil from Norse mythology. The imagery of thorny vines overrunning a kingdom isn't that new, either, just look at Sleeping Beauty, Disney version or otherwise.
Star Swirl the Bearded probably is based on Merlin: a wizard with good foresight guiding future royalty towards their destiny. Kinda like Gandalf in that respect. Heck, the current version of Spike is suspiciously similar to the titular character of 'The Dragon Who Wasn't, Or Was He?', a Dutch film from 1983. And that probably has its roots in some folklore, too, maybe Ring of the Niebelungs.
I'm sure there's an ancient faerie tale that inspired the Tribbles/Scribbles/Parasprites too, somewhere.
On a more mundane level, FiM has always been pretty Golden Age Disney-esque (or Crappy Age Disney-esque, depending on where you stand in the fandom), and Disney has always been something to copy for other franchises. That can be good, or hilariously bad and predictable if kept up too long. You can tell it's Disney-inspired because there's absent/implied dead parents in it ^^. I wouldn't be surprised if someone died in MLP's Season 5, even. (If there's any bets going on about that, Discord has the highest chance to get axed).
But anyway, enough about those magical talking horses, let's talk about magical talking horses.
I'll concede Sofia's not a horse show, I just figured it might get an honourable mention or something. I have seen the Minimus episode a few times, it's enjoyable even in the dub. The obvious moral is a little... ham-fisted, I'll admit, but I've gotten into the habit of overthinking things like that. I really liked James' character there, hlping out his sister despite the mockery.
I find it a bit odd you don't hear the name Epona more often, in general. I mean, it's a horse goddess, she was apparently popular enough to be accepted by the Romans for worship, it's a fine sounding name but it's only really used in a videogame. Weird.
>On the topic of animation colours: Do anyone else than me find Star Wars Rebels' colour palettes horrendous? I've only ever seen 4 colours in it, brown, grey-brown, beige-orange-brown, and blue.
Hmm, can't say I've followed it, because of dumb dubs and just sheer silliness, but err... maybe. I distinctly recall seeing a pink and girly Boba Fett a couple of times, though, because apparently that's a thing in Star Wars now.
I'm trying to think of other horse franchises, but the only thing that comes to mind is a reindeer one, so... That's me run dry for now.