I'm surprised they all lasted this long. Having dozens of Comic movies and tv shows have diluted comic related productions as a whole. Soon the MCU will start to exhibit the same fatigue. I got bored with superheros long ago. I haven't even watched any DC shows.
Just so much product coming out of Hollywood nowadays (more than ever before) and so much of it is superhero and scifi stuff. Who the heck even has time to watch it all??? I think the days of iconic TV shows and movies are long gone.
It is being pushed by the studios because the Superhero genre is a safe bank for now - even the bad ones still make profit, as long as that is the case they are here to stay and there's tons of material that hasn't made it to the screen. Some shows have shorter life spans and are gone after 2-3 seasons but others stay for their full 7 season run though CW will have a major problem soon when their current main series end their runs, i.e. Flash, Supergirl, Legends and they have so far failed to establish follow up shows that have the ability to stay ( i don't watch Black Lightning, maybe that show has a chance as i see here it may be good).
Also what does iconic actually mean? A show or movie that defines the genre it is in? That would be hard to do as all genres one can think of have already been established and "iconicized" - SF has Star Trek and Star Wars, comedy has a much broader appeal ranging from I love Lucy from the 50s through the 70s with Mary Tyler Moore, 80s with Taxi, Cheers and into the 90s with Friends etc.
I think Arrow would fit into this when it comes to superhero shows as it started the aptly named Arrowverse where DC reigned the TV screen until Marvel got it's house sorted and released TV material (though Shield, as good as it was in the middle of its run couldn't compete with the Arrowverse and the Netflix shows are set apart).
So the ball will roll on as long as it makes money and Hollywood truly runs into the ground but i'm in a similar boat as a big Marvel fan - that epic 22 movie run has concluded with Endgame and i can't bring up this much excitement for the new movies as i used to. Maybe Marvel can do it again and still release good new movies and form a new storyline (if at all), we'll have to see.
WB on the other hand never truly lifted off the ground like Marvel, their tentpole movies with Superman and Batman fell flat and the only ones that are actually good were Aquaman and Wonder Woman (Aquaman by the charisma of its lead and Wonder Woman by both Gadot and an actually decent story).