2x2=4
If you don't crack your Sphere early then you didn't need it and should've done something else on T2. Cultivate ramps you for one less net mana and it's in your colors, I don't see how you can pick Sphere in any green list.
Also, unless you are playing 4 or 5 colors in your deck then I'd argue Traveler's Amulet is a better mana-fixing option because it costs half as much. I also tend to beat Traveler's Amulet decks. Cultivate decks not so much.
Here, I agree with you.
I can think of more than a few decks where I would rather be running
Armillary Sphere instead of Cultivate, even using a deck running
though.
Bant Control being the most obvious answer here.
I made a post about this just the other day in the Dimir thread.
The real advantage of Armillary Shere (one which this particular deck isn't really looking for, hence why I say I agree with you here in regards to this deck) is that cracking it can occur at instant speed. I would say that in about 70% of my Control decks I would prefer
Armillary Shere to
Cultivate.
Cultivate may be cheaper, Cultivate may ramp for you, but Armillary Sphere makes sure you consistently are able to hit land drops (while also helping to fix) without the need of having to tap out and leave your opponent open to play whatever they want.
Cultivate on T3 means being tapped out when your opponent plays that Rabblemaster, or Brimaz, or Thoctar, or Rhox, etc. The same is true of turns 4+.
The real advantage of
Armillary Sphere is that it can function like a land based version of
Think Twice. Sure, we can crack it early if needed to hit land drops (much like sometimes the best use of Think Twice is to use it on your own main phase to try and ensure a land drop), but that isn't the IDEAL use for the card.
No, the card is best used when cracked on an opponents End Step on a turn in which they haven't done anything worthwhile, much in the same way cards like
Think Twice and
Inspiration are used. Except here instead of getting gas, it gets us Land. This can not only help with fixing in general, but is overall a pretty big help for decks which want to consistently be able to make land drops every turn (aka Control decks) without having to tap out so they can keep removal/counterspells/etc up at all times.