It's 100% correct that in NE or anywhere near the coast Red Lobster was always considered inferior. The local competition and the ability of non-chain restaurants to "buy off the dock" meant you could always find better options that maybe even cost less.
When I moved to Central TX, I was stunned by how much everyone loved Red Lobster. It was my MIL's favorite celebration restaurant, and my wife loved it as well. To me having lived on fresh seafood for years, it was OK not great, but you could find decent seafood, slightly overpriced. I did see a rapid decline over the next 10-15 years.
But the problem isn't market share since most of the US doesn't have coastal access to fresh seafood. It's the same thing that happens to every chain restaurant after being bought out by a corporation. The restaurant life cycle as I have come to see it.
Start off being run by an owner who cares and is invested in making good food, grow to a local chain, start franchising, grow and get bought by corporate, focus changes from good food to profit and consistency, food quality craters, customers depart.
There's no magic here besides corporate mismanagement from the unlimited shrimp deal that cost them millions a quarter in loss to moving away from scratch cooked food to microwaved prepackaged food.
It's the same with Applebee's, Chili's etc. at one point all these places were decent to good before corporate greed and mismanagement steps in and starts selling over-priced sugar cocktails and appetizer specials. It's no longer about providing good food and atmosphere to families but about extracting maximum value from a customer engagement.