It still was a recurring enemy afterward compared to the Rock Troll Heartless fought in Olympus and Arendelle and the Metal Troll in San Fransokyo. In fact I say the carriage Horse heartless is very reminiscent to the Skeleton Ice Dragons that SDG fought in Arendelle.Corona had that horse cart heartless as a midboss before you reach the kingdom
Frankly, both Corona and Monstropolis are the ONLY ones with one boss respectively with the rest of the world mostly being Mob fights against Heartless and/or Nobodies/Unversed before culminating with a final boss at the end of their respective worlds.