Regrowth is not a staple in this deck, it isn't even the reason this deck runs Green. In fact, Regrowth is a terrible card that costs tempo, it's a tutor in an off color that that has a limited number of targets. Any one who is playing this card over the 4th Grim Tutor seriously needs to take into consideration which one would actually be more likely to win you the game in any position (ESG isn't an argument, because I can say the same thing about the Rituals). Crop Rotation has way more justification to be in the deck than Regrowth, that card is the equivalent of a Blue Ritual, that is way more broken than anything Regrowth could ever do.
The only thing that makes regrowth "broken" is its usefullness in the drain matchup. In a matchup where your bombs get countered left and right, regrowth is an incredible way to recover. It might not be a staple, but it is certainly more useful than burning wish.
Crop Rotation, while incredible in goldfishing, can leave you hurting when it is countered. Of course this can be played around, but I think the whole Regrowth vs. Crop Rotation is a metagame call. Against Stax/Fish I'd go with Crop Rotation. Against Gifts/Slaver, I'd go with Regrowth.
Personally speaking, I prefer 8 Rituals because of the increased odds of resolving Grim Tutors, Necropotence, Yawgmoth's Bargain and their synergy with Duress, when I bother to play the card, and Demonic Tutor, Vampiric Tutor and Imperial Seal. Honestly, I can't understand why any one plays with Elvish Spirit Guide, because the increased odds of resolving a Draw 7 are worse in comparison to the black cards, they don't have synergy with Duress, Demonic Tutor, Vampiric Tutor or Imperial Seal, don't produce 5 mana with Threshold and can't be replayed off a Yawgmoth's Will.
In theory, what you say makes sense, but after playing with 4 Cabal Rituals, and a Burning Wish for a while, I realized that Cabal Rituals just made too many bad opening hands. Many times, Cabal Rituals wouldn't become active until turn 2, and other times they were just sub-optimal. This led me to the decision to run 3x Cabal Ritual 2x Elvish Spirit Guide. This minimized the number of bad opening hands due to Cabal Ritual's casting cost, and still retained Cabal Ritual's "consultability". In other situations, ESGs made Cabal Rituals playable.
Burning Wish is protection from Extract and Cranial Extraction, a tutor for Tendrils, a second Yawgmoth's Will and removes all of the same cards that Chain of Vapor does. It is a bit of a trade off, because you lose tempo to wish for an answer, but that answer is both far more powerful and permanent, like Balance. You don't get to generate storm and mana either, but when you consider that you have two additional paths to Tendrils, Demonic Consultation, virtual immunity to Extract and Cranial Extration, it can't be countered with Chalice @ 1 I say it is easily on par with Chain of Vapor.
Again, Burning Wish, in my testing caused too many bad opening hands, especially with the two copies of Tendrils for Consultation. The double Tendrils already solves the Extract problem, and Cranial Extraction... not run very often. At all.
Overall, removing cards like Regrowth, Elvish Spirit Guide, Xantid Swarm, and Chain of Vapor improve your game goldfishing, but in actual play, these cards can be vital. I would sit across from a good control player for a while and reexamine your card choices.