Actually, the show that really changed the TV narrative was The Sopranos (1999)...nine years before Breaking Bad (2008).
And it's still arguably the best TV series ever. I love Breaking Bad as well...but can't beat the GOAT, imho.
Others have mentioned Mad Men, and The Wire as the best TV series of all time. I think those 2 shows certainly belong in any objective top 10.
If this question was asked back in around 1980, many people felt that "All In The Family" was the best TV show of all time through that date. I would say that either that show or "MASH" were the top shows of the 1970s.
For the 1960s, in addition to "Star Trek", which was an iconic show, I would mention 2 others: The Fugitive, and The Prisoner. The final episode of The Fugitive in 1967 was the most watched episode in the history of television for a very long time. The Prisoner only lasted 1 season/17 episodes, but it's a truly brilliant show and the final episode was among the most discussed final episodes of all time. Batman was the first TV show to combine live action and animation and was quite creative, though it was campy and not taken seriously by TV critics at the time, but is now considered creative for its era.
The Cosby Show was probably the most successful TV show of the 1980s, but nobody will say that now because of the demonization of Bill Cosby for his various alleged criminal behaviors which came to light years later.
For the 1990s, Seinfeld and X Files.
For the time period 2000-2022/21st century, I go with Mad Men, The Wire, Breaking Bad, and Better Call Saul. Regarding the Sopranos, as I never got HBO, I never watched it, but it is my father's favorite TV show of all time, and he has seen all the ones I mentioned, so it has to be on the short list. I did see the Netflix Sopranos spin-off "Lillehammer", all 3 seasons, and I enjoyed it.