Undersell, over-deliver? Let’s look at their track record since Diagon Alley:
Kong - an okay experience, absolutely no one is blown away by it.
Fallon - not good, and completely cheap and lazy and overkill for a park with multiple theater-based simulators already.
Volcano Bay - “the world’s first water theme park because it’ll just be THAT immersive you guys, no seriously!” Oh wait it doesn’t even live up to Typhoon Lagoon or Blizzard Beach (for theming and immersion at least)
Fast & Furious - objectively one of the worst rides ever made.
Hagrid’s - yes it’s a GREAT ride but it was touted as “the most immersive roller coaster in the world” but it falls short of many, has numerous obvious shortcuts and budget cuts taken. It doesn’t live up to the detail immersion of the rest of the WWoHP.
So yeah, lately it sure seems like Universal’s approach is “promise the world and then go 3/4ths of the way”. If each land in Epic Universe is, say, on par with Diagon Alley, then yes, it’ll be exciting