They start with a man and woman co-staring, they add every race and many many religious beliefs and difficulties that are still talked about today. The show is amazing and shouldn't have ever stopped. However when they finished, they finished big. How can anyone compete with that? The UFO report list shortened after it stopped airing... it is amazing as a show and could never again be duplicated. I sincerely love the show and I watch it on repeat because it's perfect for what it is.
You're assuming a lot of things are timeless that really aren't. Given the prevalence of remote working and employment these days, do you think the idea of an office building is timeless for when they destroy one? Will people wonder why that wasn't a condo building? For infrastructure depending on trains transporting so much, would it not seem odd to track down a train transporting some alien substance if trains are no longer used because of new transports?
The speculation of "completely timeless" seems wildly inaccurate when thinking about just a few scenes from the movies, let alone the series.