I can't find any fault with your reasoning. I have to say I LOVE Blue Man Group (have seen them 4 times), and I have also seen the water shows (Eau or "O" and "La Reve" at the Wynn in Vegas) that the Oasis shows are based on.
I normally would NOT take a cruise for entertainment - but by the same token, I don't go to Las Vegas for entertainment either, but in Vegas you have to pay for it! On a cruise ship its "free*" (included in the cruise fare).
If I were in Vegas and the shows were free I would certainly go. I have paid $100 for Cirque shows in Vegas, I have paid $100 for tx to Hairspray (the roadshow) here in Phoenix and the venue was awful. It is excellent on Oasis.
I think if you saw the shows on Oasis you would think a little differently, like "finally they are getting the entertainment on cruise ships right."
But the other things you mention; flo-rider, rock climbing, ziplines, eyc, I dont need those either, but I can watch people do them. I don't need to do a lot of things, but I can enjoy them.
I'm just wondering what cruise lines you prefer, nancy?