One most distinct feature of MMOs is that there are 1000s of players online in the same world, the chat is 1000s of players, the economy and auction house is all 1000s of players.
Focusing only on one aspect like "groups are only a few people or PvP is only 3v3 and 6v6" is cherry picking to make your flawed argument.
so no - this game IS NOT an MMO
That is the old way of thinking of the MMO genre. This is the new way...
Games like World of Tanks, League of Legends...lots of games...all those are considered MMOs by many. That is the new MMO genre, it evolved into games like Mass Effect and LoL and WoT and many others.