I honestly don't get your arguments here.
On one hand you are arguing against using IP, that it's the IP that ruins things. But then go on to complain you don't like the ride itself. One really doesn't have anything to do with the other. If you don't like rides that utilize screens (your comment about Rat) then the IP really doesn't matter. Its the ride system you don't like.
As for not liking the new rides, that's simply a subjective opinion. I would put RotR and FoP up against any ride in the country and be very happy with them. I didn't ride GotG personally, but the rest of my family did and had similar comments for it. And this is where the difference in IP comes in to play. I have heard nothing but good things about Velocicoaster. I don't ride roller coasters but everyone i know who does, and has ridden it loved it. BUT no one made their decision to go to universal to ride that coaster. Those people (at least in my area) can ride roller coasters of better, or at least relatively equal quality (subjective of couse) at Hersey Park, Six Flags, Bush Gardens, Old Dominion, ect. Everyone i know who rode Velocoaster were down at Universal to see Harry Potter.
As for Epic Universe/Universal, they are following the same plan as Disney. The new park is leveraging established IP, either Nintendo or Harry Potter in the same way that WDW is using Frozen/Star Wars/ect. As for when EP opens, I will say having done both Nintendo rides in Japan, I don' think they are a big challenge to anything Disney has. I mean sure Yoshi's ride was ok once as I got to say hey I remember insert character here from the games I played as a kid, but that was basically it. I don't think I would ride it again and again, the same way I would haunted mansion for example. And while Mario Kart was OK, I don't think i would go beyond that. The people who was with who had no connection to the old Mario brothers games didn't find them to be anything special.
Which is really the whole point everything being equal IP drives your customers base. You like Harry Potter, your going to Universal. You like Frozen, your going to Disney. And by offering rides on that model you have a competitive advantage that no one else can beat. And for those that just want rides and thrill, they can go to [insert local regional amusement park here].