Hey Tucker... what confused you is that people probably referred to down picking using up more energy and is a lot harder to work up to speed. So, down picking is much more simple as it only requires you to pick one way but when you try to pick faster using down strokes it is harder and that's when people choose alternate picking.
Using alternate picking is more efficient but ultimately is a lot more complex when you start getting into crossing strings etc..
It all depends on what you're using it for as well. Down strokes are great for playing riffs and even for certain lead lines where you want an aggressive sound but when you're playing anything of a moderate speed and crossing over strings it makes more sense to use alternate picking.
However, certain players like James Hetfield of Metallica uses down strokes to play riffs that most guitarists could only do using alternate, because it uses so much stamina. So, if you want to be able to play fast, chuggy metal riffs then increasing your down picking speed is a must. Either way, if you're working on lead, you should delve into the world of alternate and embrace it