It's a generally accepted date in the TV industry; most use that show as the first one to define the era.
There again, who is doing the defining? What age group do they represent? Most likely most are too young to have watched shows from well before they were born.
Some of the shows like "The Sopranos" and "Breaking Bad" were indeed outstanding. BB is my all-time favorite show. The Las Vegas CSI shows with William Peterson are excellent.
But overall, tv in the last twenty years has been overwhelmingly crap.
The crap to good program ratio has always been heavily weighted on the crap, but not as bad as it has been in the last twenty years.
When I can't find one decent series on network tv that isn't dull/too p.c., things are pretty bad.