I guess I should’ve phrased that better. While SU is more sci-fi than magical fantasy, those supernatural elements (gem creation, Great Diamond Authority, fusion, spaceships, warp pads, ancient temples, etc.) are still more believable and feel better thought out/organized by the show’s writers and artists as opposed to the nonsensical clusterfuck of SvtFoE’s rules of magic and worldbuilding.
Shit like the Pony Heads, the Royal Magic Wand housing sentient spells with average lives, or Mewni being referred to as both a kingdom and a whole dimension just makes it seem like Daron’s original pitch for the show simply revolved around a “magical princess from [a vague, magical other dimension].”
At least half of SvtFoE’s worldbuilding was probably created on the spot in the middle of writing Season 2. The show is somehow worse at making a believable, structured fantasy setting than fucking Adventure Time. Also, it really isn’t that funny a lot of the time.