I'm going to put my Misfit comment in spoiler tags as it's technically off topic xD.
On the subject of the sea ponies, sort of. There was King Neptune and Miranda the Mermaid. Also Kelpie, who was some kind of water sprite I think, drawing on some local mythology I believe. The adult sea ponies didn't much appear in comics but there were books with the ones we had here in - Surfdancer and the Little Mermaid was a talking book (the only one for which I can't currently find the tape, grr) and they also appeared in either the Man in the Moon or the Stolen Shadow (though they are not named right in every edition). Seaspray weirdly had a boat. I don't know why or how that makes sense, but she did.
The baby sea ponies had more of an innings as they timed better with the comic being out. They all had distinct characters, especially the originals. Tiny Bubbles was something of a leader, Splasher couldn't actually swim or didn't like actually swimming but splashed around everywhere (they had the floats because they were all learning to swim but Backstroke was supposedly an excellent swimmer already). Sea Shimmer was the naughty girl always getting herself into some kind of trouble or adventure. I can't remember with Surf Rider. The pearlies appeared less but I remember Water Lily was a dancer and performed water ballets. I know Ripple and Sunshower did have characters as well but even though they were my childhood ponies I can't remember :/
Spoiler
Pizzazz and the Misfits:
Pizzazz is not a 'princess' type nor really comparable to the princess trope. She's not really spoiled so much as she has everything material and nothing emotional from her father. You see that especially in Father's Day where she can't believe Clash's father really loves her and then is kind of destroyed by Harvey showing Kimber more attention than he does her. I think Pizzazz just wants to be acknowledged by her father. It's not the same as the spoiled brat princesses who just want attention without any deep dark reason why they behave that way. The Misfits in general are very human flawed individuals driven to extremes by circumstances. I think Jem herself is a better candidate for the rich kid princess character. More so than Jerrica, because she has the real world hassle, but when she's Jem, there's a sense of irresponsibility about some of her actions (like taking off with Riot on a sea trip and leaving everyone else in the lurch). Even Jerrica doesn't understand the issues of the runaways until some of hers run away in Music Awards. Pizzazz also isn't a snob. Jem and the Holograms are really mean to some of the regular folk in the show (they criticise the gondola driver in Venice for not wanting to give them a free ride, they are also negative about a rough-around-the-edges nightclub and they are flat out mean to the poor slow guy at the garage in whichever episode takes them there...Stolen Album possibly). Pizzazz goes to all these places, irrespective of the fact she's rich. (Plus she spends most of her time with Roxy and Jetta, neither of whom come from that rich vein of society. Jem and Jerrica do not mix with those people unless they are "helping" them (see the horror that is telling people who can't read to read without actually teaching them to read). That's a little different from the Princess Ponies.
In my opinion Pizzazz has much more character depth and development than the Princess Ponies do in their episode, and so the two things are entirely not comparable.
But I am a Misfit fan ;)