Doesn't sound like you expected change to me. A 19 year span is a LONG time. You really weren't expecting some major differences after almost 2 decades??
Did you check out the website prior to your current visit? Perhaps email or call to find out if the flamingos (since they are not mentioned as a park feature) was a guaranteed interaction without the add-on experience?
I can tell you that we visited Hollywood Studios in October for the first time since 2009. I expected major changes since that last visit. And I did my research before we went so I knew exactly what I was getting.
Several years ago, on one of our Discovery Cove visits, they had an animal care staff member in the check-in area holding a sloth. Guests who were arriving for their all-inclusive day got to meet the sloth, pet her, take pictures, etc. It wasn't at all promised as part of the DC experience, but just a happy bonus on that particular day. Just because it happened that one time didn't mean that was a guaranteed interaction on every visit.....and we've never expected it to be. You got lucky (blessed? pixie dusted?) with the flamingos. You should be counting your blessings rather than complaining about what they've "taken away" .
Discovery Cove runs promotions ALL the time. In 2012, we snagged day resort admission for $69 per person. In 2018 (? I think) we were able to get the day resort admission for $89 (I can give you exact dates if you really want to quibble, as I keep a record of what we spend on every trip and add it to our photo books.....it's fun to look back, 20 vacations later, and see how prices have changed over the years). So $112 each is actually "expensive" in my opinion.
FEEDING the rays is not included, nor has it ever been. Snorkeling with the rays is what you are referring to, and yes has always been part of the DC experience. FEEDING the rays is a new add-on animal experience that can be purchased....or not.....at each family's discretion.
If it's not advertised as a park feature, it's not "included in the price".
Snorkeling with the rays is referenced on the website as an attraction/included experience, and should be expected by all guests.
Same goes for access to the lazy river, feeding the birds in the aviary, seeing the marmosets and the Asian otters in the Freshwater Oasis, breakfast, lunch, snacks, drinks, etc. etc. The things you can expect are very clearly laid out here:
All-inclusive Experiences - Swim with Dolphins | Discovery Cove
Your disappointment is in expecting something special that was not promised to you in the first place.