My hunch is that this wouldn't work out, but do you think there is any merit to Orb of Dreams as a form of disruption in this type of deck?
You speculated that Sphere might be necessary in the board for some match-ups, like combo, but I wonder if Orb could be a better choice. Both cards are comparable in that they both slow down combo/fast starts from the opponent, but also can slow you down, too. However, I think Orb may have some advantages that are at least worth considering.
Let's get the obvious out of the way and point out why Orb would seem be terrible here: you don't want your mana rocks coming into play tapped when you're trying to go off, it doesn't do Sensei's Divining Top any favors, it can impact the game less if you're on the draw and the opponent drops a bunch of mana on the first turn, and it's more expensive than Sphere. Those are pretty serious drawbacks.
But I do see a couple of potential benefits.
The main benefit, I think, is what it does to the opponent's creatures. If you can't go off and kill the opponent, you can drop this and prevent your opponent from building an effective mass of blockers or lethal counterstrike (sorry zombies and Vengevines, no blocking/attacking for you). Sphere won't do that.
Another benefit is that Orb could be more immediately impactful than a single Sphere in some circumstances. For example, a single Sphere does not prevent the opponent from playing an untapped Black Lotus with a single land, or even playing an Academy, and hitting just enough mana to do something relevant. Although Although Sphere has the advantage of impacting the game for longer, Orb can make the bigger impact for a shorter period of time, which seems more important for a deck that's not in it for the long game.
Perhaps using Orb would require a substantially different list that tries to leverage its effect more fully, like adding in Jhoira's Familiar or Helm of Awakening so you don't really care if your mana rocks enter the battlefield tapped or having additional sac outlets beyond Ravager to manage it better when you are trying to go off.