So, in conclusion: ranger should have its subclass kick in at 1st level.
No. What Mearls is saying is that classes like ranger and paladin should either have their 1st level abilities buffed or their subclass moved to 1st level.
If rangers are supposed to be a class with exploration good skills, standard weapons and armor, and a combat trick, then Favored Enemy and Natural Explorer need a buff.
If rangers are supposed to be a skill monkey that trade some skillpower for weapons and a decent AC who later develops more combat features then it's subclass need buffs.
The issue is the designers didn't choose which one. Ranger sublasses are both specializations and definitions.