I don't feel that way. I think you could take 3E WotC FR Books and place them next to the SCAG, and you could objectively prove it is a lower quality book. If you still have those old books, read both, really dig in and peruse an old WotC FR book and then read the SCAG. Then get back to me about their quality as far as the bang for the buck you got from each book. Look over the crunch and the fluff and compare them. Then tell me that they are equivalent. I'd love to see a true analysis.
I still have my FRCS from 3E and I love it. Still use it. My campaign is based largely around the FR setting at that point in the timeline...i.e. Shade Enclave hovers above Anauroch, the time of Troubles was twenty-ish years ago, and so on. I don't need another full fledged setting book.
Having said that, I still bought the SCAG. The reason is that I wanted 5E crunch for certain Realms specific ideas like Purple Dragon Knights and so forth. I also liked to read the fluff material, even though I'm essentially disregarding anything related to the Spellplague or Sundering. I may pick and choose some things from the newer era...the presence of dragonborn and things like that...but it'll be on a case by case basis.
What I think it excels at is as an introduction to the setting in a palatable way. My players don't follow the Realms as closely as I have at times. They'll find the book invaluable as a resource. If they need to know about a country or a god, they can read the entry in the SCAG. I just have to keep in mind that some things have changed compared to my version of the Realms. But hey, most f the book is written in an unreliable narrator type of tone...so anything that doesn't jibe can be explained away.
I think the value as an introduction is overlooked by folks who don't need an introduction to the Realms. Compared to the 3E era books, this book is less useful for you. That's fine...I understand why, and I respect that stance. But to say that it is objectionably so? That just seems wrong.
A few months ago, if someone new to the hobby came here and started a thread asking for a good source to understand the Forgotten Realms Setting....imagine the replies. People would be all over the person citing the sourcebooks and novels that they personally like. "You have to read the Avatar Trilogy" or "You have to have Faiths and Pantheons" and so on. It'd be an overwhelming amount of information that no new player would be able to properly parse.
Now however, we can simply advise "Pick up the Sword Coast Adventurer's Guide" and that would be a sinple solution, requiring one book. The player could then proceed from there for further reading if they wanted.
So...putting the books side by side, I find that I like each just fine, for different reasons.