Easy (not really) fix - pull a KD, hire an exec chef and restaurant-oriented kitchen crews vs. the watered-down convention food service on a budget mindset they have cooking now, and also like
@Zachary indicated, give them a reasonable budget to make things happen.
Fuck yeah use the show grill all the damn time at Trappers, make some crazy grilled stuff with it. Get a couple of them bigass wood burning pits too, and put on a show. Hell, make burnt-ends and pork belly bites as a quick serve option right to the side of that grill with all the platters, sides, drinks, etc being available in the main lines.
FestHaus - just bring back the mile high sandwich, sausage platters, the warm potato salad and cabbage stuffed, and reopen the line for pizza/fries. Don't need to get too innovative with it, just tasty and filling stuff for not crazy stupid prices.
Marco Polo's central theme is noodles across cultures (such as Chinese origins of spaghetti and so on). If they realistically can't scratch make much of the pasta, at least they can showcase local ingredients and make their own sauces/toppings/broths. Tbh I like where
@warfelg's head is at - if there were ever a place for decent scratch-made pizzas in a park (going from your standard Costco toppings to eventually specialties based on the theming - Chinese pizza could be a good thing), this would be the spot. The only thing they'd want to do is a showpiece clay/brick pizza oven if there isn't already one there (been awhile so my memory is a bit hazy).
Put some hearty stews and soda bread in Killarney for those that want to eat, and the Trapper's crew can smoke some corned beef for service as well. Plus, decent and cheap quick-serve pub food too, such as fries and Irish nachos.
Banbury Cross keeps Squire's though should be similar to a peanut-free 5 Guys. Dead simple in execution, can quickly get good burgers and fries out during a rush, and allows for some level of order customization. Or go In-n-Out on it... Not too much different except there's less to customize. Also, given the strong connection between Britain and India, an Alehouse location where one could find cask-aged bitters and lagers, of course IPAs, and some options for fish and chips and curries. And of course, bangers and mash... And mushy peas too.
Festa... I'd hope they'd lean towards a Greek retheme, but barring that you have two Italies. So perhaps maybe do some kind of generic Mediterranean concept, something similar to a Kava or Mezza where there's several options of fresh-prepped foods to be layered in a bowl over rice or greens.
Bring back the smoked jumbo turkey legs and fresh popped kettle corn, if it isn't there and I just missed it - used to be some pop-up stalls and they had some at the quick-serve in Aquitaine.
... And not sure where the best location for this should be, but riffing on a Chopt salad bar concept would be a good option for a relatively inexpensive but high margin eatery.
Almost all of these ideas are proven concepts somewhere, if not having been proven right there in the park during the AB years. But it'll take time and money along with the right leadership to make any of that happen.