Being able to cast creature cards from the top of your library is already strong, and you can cheat big creatures into play once per turn, and not just from your hand in a clunky way like Elvish Piper does
Since then numerous iterations of split cards have appeared through the years, with the original split cards themselves making occasional comebacks every now and then
I think this set knows what it's doing: hook you with Kanto starters, then keep you around with glittering, high-rarity flex pulls
It can even remove five +1+/1 counters to add two of each color of mana to your mana pool, allowing you to mutate multiple times per turn easily
But since Instants never enter the battlefield to begin with, legendary Instants and Sorceries work slightly differently
I also dont have much experience with vintage WOTC-era stuff, which I imagine is also quite liquid