GSZ is a significantly higher mana commitment than Cage. GSZ also requires you to run several green creatures that may or may not be useful if you draw them naturally (see Thornscape Apprentice). Perhaps most importantly, GSZ does not answer Yawg Will to any meaningful degree unless you run Loaming Shaman or something. GSZ for Ooze will not necessarily beat Dredge either, again due to the high mana commitment and the speed of Dredge. Finally, GSZ only fits in one deck while Cage can fit in literally any deck.
Ooze is good against Y Will. I overlooked that in my initial post. Sure, GSZ needs mana, but you are naturally running noble and should run scryb ranger.
I believe that GSZ is much stronger in Legacy and probably too slow for Vintage. I believe that for the exact same reasons why i think that Scryb Ranger is too slow in Vintage.
Additionally building the deck around GSZ it means that you are accepting that you need more mana and more turns to develop your full strategy and you are moving towards building a midrange deck.
This is not a bad thing, but it needs to be supported by counters that allow you to get to the mid game ! I would see the GSZ much better fit in a Zenith BANT deck than in GW.
Ranger is extremely powerful in GW beats with some bears that have tap utility or need mana to activate (Thorn, Ooze, Noble). I tested it extensively and wrote about my observations in several threads. You still don't believe me, time to test them out for yourself... You need to understand the role of the card, it is not about speed, it is about control. Besides, it IS an accelerant a lot of times... like euhm Lotus Cobra for example, if left unchecked, you just play out your hand.
Turn 1 Noble pass is not developing your mana base and seting up strong turn 2 and turn 3 plays? What I do is use Thalia, Stony, Aven, Missteps, Wastelands early on to disrupt the opponent. Depending on my hand I sometimes get a Dryad or Noble early on with GSZ but that is usually not how things go. After the initial disruption you get in whatever you think is cutting them off from recovering. That can be Ooze, Thorn, Teeg, Pridemage (Will, Tinker, TV, Jace, Gush, Tendrils...) it depends on what you have what they already played etc... You aren't getting Thorn when you have Aven against a blue deck with Tinker. If their grave looks juicy for a big Will or Snapcaster you get your Ooze. These are the obvious lines, it can be more complex and hard.
GSZ is a great utility card, but it really is awful as a fast answer. If you have a thalia, noble, or whatever in play and your opponent responds with an oath, you can gsz for thornscape, but it will be too late...tidespout, demon, maniac, hasty bsc/emakrul...you'll be toast first. A 1 mana answer is an answer with speed, that can be played proactively (or reactively in the case of oath). It also stops snapcasters, yawgwills, welders, etc. No WAY you race dredge with GsZ->ooze. I rarely even win with turn 1 tinker->bsc vs dredge...no way you can get 3 mana, untap, then eat their grave with enough green mana to be relevant. Yes, you have wastelands and such as well, but if you always have ALL your answers in hand, do you really need GSZ anyway? And plow/mistep are not answers vs dredge unless you are fighting hate that would kill your cage.
GSZ is not acceptable as an answer to these cases. On occassion, you may get a lucky situation where the card you fetch can control things, but more often than not you'd wish you had cage instead.
You get pridemage vs Oath. Lot's of them

I don't know how many times you played GW beats verses dredge, but GW can really stall for a while with Thalia and Wastelands in game 1. If you happen to find mana and buy A LITTLE time, that GSZ> Ooze will take the game. You do need some luck, a mox for example and a wasteland to gain a little tempo. Also, if they lose bazaar and don't get a lot dredgers, this can mean you get that small window. I would not dream of beating a broken dredge hand, but who does anyway g1..

I also noticed that GSZ enables me to keep hands I ordinarily could not keep. This is because of GSZ>Dryad or Noble.
And I do think GSZ has more than 1 home. Midrange Bant Zenith is not a beatdown deck and usually runs 1 or 2 GSZ. That being said, GW Ranger beats is not a classical beatdown deck either. I would call it midrange beatdown.