This topic is really 50/50 and any point can be proven right.
I personally think that for a era, they have to make something no one has ever done (for example first 16-0 at Major) and is just amazing. They have only one major if i'm not mistaken, so only the 16-0 at Major makes them shine.
It might sound fanboy, but whatever.
Compare this, to NiP era. NiP have made something a lot of teams dream to do.
Yes they have only one major, but the fact that they've dominated cs day in and day out, made them have a era.
Fnatic had a era, 3x Major. If i'm not mistaken, that makes them the best cs team in terms of achievements.
SK is a bit 50/50, but they were DOMINATING made them have a era.
Astralis are a good team, but the quality is average at most. I think if they can get a major and show dominance, we can talk about era. but atm i think they can be talked as the 16-0 Major makers