Can you explain what information you're using to make that claim in bold? I'm not saying you're wrong, but I'm not sure this paints an accurate picture, historically.
Is it really overbuilt, though? I think I have to dispute your count, or at least I'd need to know more about its methodology, because Magic Kingdom and Epcot definitely have more quick service locations than you're stating here.
Marvel, Jurassic Park, and Toon Lagoon have two indoor quick service offerings each (Cafe 4/Captain America Diner, Thunder Falls Terrace/Burger Digs, Comic Strip Cafe/Blondie's). Seuss Landing and Hogsmeade have one each (Circus McGurkus, Three Broomsticks). Lost Continent has none, and I'd hesitate to call Crescent Moon Bakery in Port of Entry a true indoor quick service restaurant.
Food windows like Wimpy's, Fire Eater's, and Green Eggs and Ham may offer entrees, but I don't think that qualifies them as a full "restaurant" per se.
There is absolutely no way Epcot and MK can have only 6, especially if we count places like Fire Eater's for IOA.
I'd qualify a quick service restaurant that serves 'full' entrees and has some form of seating as quick service. There's some venues that blur between lines, so it's hard to truly provide a 1:1 comparison.
Historically over the past few years the quick service establishments I listed have lacked later operating hours. They'll occasionally open one or two later in the evening, but rare. Can't remember the last time Thunder Falls stayed open late outside Spring Break/Holidays.
I don't think my list below is inaccurate. I wouldn't say something outrageous without checking the data first.
I read the counts for Epcot and MK and thought I was going crazy for a second lol
You are not going crazy. We can debate whether maybe a place like Sommerfest should qualify, but it has like 2 tables and one bratwurst option. I include Fire Eater's as quick service since it has a plethora of options, seating and acts as only 1 of 5 dinner options available.
WDW
Magic Kingdom (5): Casey's Corner, Pecos Bill, Columbia Harbour House, Pinocchio Village Haus, Cosmic Ray's (used to be 6 with Tomorrowland Terrace)
Epcot (6): Connections Eatery, Sunshine Seasons, La Cantina de San Angel, Lotus Blossom, Regal Eagle, Katsura Grill (park has a lot of snack stands and table service, but doesn't actually have that much traditional quick service)
Hollywood Studios (8): Backlot Express, Dockside Diner, ABC Commissary, PizzeRizzo*, Dockign Bay, Woody's Lunch Box, Rosie's All American, Catalina Eddie's
Animal Kingdom (6): Flame Tree, Pizzafari, Satu'li, Harambe Market, Yak and Yeti Local Food Cafe, Restaurantosaurus
UOR
USF (6): Minion Cafe, Mel's, Louie's, Richter's, Leaky Cauldron, Fast Food Boulevard (excluding Cafe La Bamba)
IOA (11): Cafe 4, Captain America Diner, Blondie's, Comic Strip Cafe, Wimpy's, Thunder Falls, Burger Digs, Pizza Predattoria, 3 Broomsticks, Fire Eater's Grill, Circus McGurkus
UEU (9): Toadstool Cafe, Pizza Moon, Oak & Star, Meteor Astropub, Das Stakehaus, Cafe L'air, Le Gobelot, Mead Hall, Spit Fyre
If there are any venues I'm missing, please let me know.