Let's take the "tracking light sources" thing for a moment and pick it apart.
Now, first off, half the party probably doesn't even need a light source - they have darkvision - so, even at first level, the exploration pillar element only applies to half the party. Then, we get into mundane light sources. A torch, sure, lasts for 1 hour. You're going to need quite a lot of those. But, by 2nd level you can afford a lantern pretty easily. Now, you have 6 hours of light per pint bottle. 4 bottles a day if you really want to keep that lantern going all the time. Let's say 3. How long is the group actually going to spend in the dungeon? Two days? Three at the absolute outside? I mean, a 2nd level party probably isn't even up to camping in the dungeon if they can avoid it, but, sure, 3 days.
A gallon of oil to power a lantern for three solid days. Not exactly hard to carry.
Now, let's add magic into the mix. Let's see, cantrips: Light, Dancing Lights, Produce Flame, so, every caster save Warlocks can completely bypass the need for tracking light sources.
This was the point made much earlier in the thread. The reason that exploration in D&D is largely ignored is because it is ridiculously easy to bypass. To the point where it can be pretty much assumed that the party will have the means to bypass nearly all the elements of exploration. Need to scout - well, we've got this flying familiar that can UAV all around all day long. Makes getting lost pretty hard. Need to sneak? There are a shopping list of spells that put rogues to shame. So on and so forth.
The problem with the 5e DMG is that it in no way actually accounts for this. They talk about setting up "interesting encounters" in the wilderness, (DMG p 106), and talk about setting a "marching order". But, absolutely no advice on how to deal with the mountain of resources that your party very likely has to bypass any challenge you want to set out. Oh, noes, there is a narrow, rickety bridge. One Tenser's Floating Disk Ritual later and poof, we're across the bridge with no problems.
The 5e DMG is written with the idea that the group will never actually use any of the renewable resources it will have available. For some bizarre reason, all the advice seems to be grounded in the assumption that groups will consist of 3 fighters and a rogue.
