I think your memory is playing tricks on you. For one thing the Sopranos ran for three years alongside Lost and for another, the ‘prestige successor’ is definitely Mad Men.
Lost definitely benefited from TV becoming bigger but I think it was only bigger because it was also a major network show. Including Dominic Monaghan in the cast helped a lot and it may have been first big show to pull in film talent - I note Glenn Close joined The Shield in 2005. (I feel like this move from film to TV is really what created that thing of TV being taken far more seriously.)
I guess Lost might be the last massive Network TV show, though?