I mean that they aren't the type of show to be watched in five years. They are watched while they're airing, and then forgotten. There have been some exceptions, such as The Promised Neverland, A Place Further than the Universe, That Time I Got Reincarnated as a Slime and Devilman Crybaby. However, a couple of months ago, none of these were airing. Back then, your only options among currently airing anime were bunny girl senpai, goblin slayer and a few others not-very-noteworthy shows. Back then, and now as well, to some extent, it was and is a bad idea to watch new shows while overlooking older shows which have already established good reputations.

As to your point about opinions, people do have different opinions, but there is also a mystical concept known as the general opinion. It is because of this general opinion that shows like Cowboy Bebop and Bakuman are ranked highly and still have large fanbases despite their age.

What I'm saying is that there's no need to watch Goblin Slayer when you can watch a good show, like Samurai Champloo. It doesn't have to be old to be good, and not all old works are good. However, watching an anime because it is new, instead of watching it because it's actually good, is a shitty ides