A tier can be 1 team, a few teams or 10+ teams. It all depends on the situations and teams you are trying to compare.
Do you really think that the 10th best team in Formula1 are the same tier as top3 (Mercedes, Ferrari, Red Bull) ?
If we look at the current csgo scene i would say:
Tier1 = Liquid, vita, astralis, ence, NRG
Tier2 = Faze, Furia, Navi, G2, North, Mouse, NiP, Fnatic
Renegades and Mibr are somewhere between Tier2 and 3 (Renegades are in bad form and Mibr need a new 5th and stability). NiP and Fnatic might even be tier3 with their current form. Heroic also somewhere between tier2 and 3 but they should probably "start off" the tier3 list.
If you have a more "strict" sense of the tiers, you could say Liquid was the only tier1 team - since being in the same tier is about being somewhat at the same level.
North has 201 points and are top10. Liquid has more than a 1000 (its capped at 1k). So liquid has 5 x more points than North (and 4 x more than G2) but you wanna claim that they are at the same level or at least very close?
You see what i mean?
Just wanna add that im not trying to disrespect G2. They are on the right path, getting better and better and hopefully they are an established tier1 team fighting for titles soon. Who wouldn't like to see shox and kenny win some throphies again?!