Yeah, for some reason I didn't expect the goalposts to move forward with each expansion when it came to raids.
Don't know how I got that idea into my brain, but I figured that all of the raids would stay as lucrative end-game activities regardless of player level, but in reality they're level-gated like everything else (though with hard modes) and drop their own resources - ones needed to upgrade the gear they drop.
I thought they would drop from raids as well, at random, as with Nightfalls. I still think they should.
There are four sources for etheric light, two from PvP (Iron Banner and Trials) and two from PvE (Nightfall and Prison of Elders). As a PvE player, what I find really odd is you only get etheric light from the level 34 or 35 PoE. I thought it would drop at 32, so you could progress up from there to the 34.
A month out from HoW I have one character at 34, and it's due to a mix of an exotic piece, one Variks item, and two etheric light (two drops across 12 Nightfalls). It's a really weird way to level.
Luke said they are re-architecting the endgame with Taken King; hopefully progression is rethought from the ground up as well.