Your role xp can sometimes come very late - I solo most of my characters to mid 20s, and still usually don't get role xp til 30-40. Other imm xp is hit and miss, and you can be an active caballed hero and still go a couple hundred hours without it. But yeah, once your character is old enough, you've probably seen enough things and pked enough people to get a decent amount of edges. The problem is, the faster you get the edges the more powerful your character becomes.
Obs/explore xp is something you can control, and if you take the time to look around early on you can manage to have a couple good edges before that role xp even comes. Depending on the edges, you can make the mid levels go by much smoother and may not lose as much (or any) con pre-hero. You may also rack up more kills on the way to hero and earn more edge points as a result.
This is along the same lines as why people master skills at low levels even on something like an arial warrior. Sure, you're going to master defenses and certain weapons by the time you hero just during ranking, but your character is going to be much tougher if you do it early on.