Interesting thought, for sure.
I could well be wrong and I'm happy to be corrected if this is the case, but I don't think there are that many decks that are considering running both. I think their purposes and effects are vastly different, so I don't think it's really a case of "I'm better off casting Rendezvous than a Wheel" in my opinion.
I completely see your point that, based on the numbers,
Secret Rendezvous offers less potential upside for your opponents, and that upside is at a much lower ratio compared the upside you are getting.
I'm just not sure how many decks there are out there that are going to be picking between the two.
Wheels tend to feature in decks that can abuse them or for mono red decks that just want more cards in hand and hope to kill their opponents before the cards they've been given matter. I'm not sure how many decks that run wheels will also have access to white, but I don't think it will be many, apart from maybe some 4/5 colour cEDH decks, where rendezvous isn't good enough anyway.
If you are in a deck that wants to run wheels, the cost of inclusion is so low because of their potential pay off that they are always the right choice, even if you have to occasionally cast them the "wrong" way. I personally think that the disruption that comes from making your opponents discard their hand is an underrated effect, especially if you can do it early on in the game. For every "sweet, seven new cards" there seems to be as many "aww, but I like my hand", especially with the amount of card draw and tutoring that happens in your average EDH game. Most peoples hands tend to be fairly well sculpted. Not to mention that the players will likely have formulated plans based on what is in their hand, so even just the
mind games that come from wheels can be effective.
Rendezvous is most likely going to be used in Group hug or White-X decks that struggle for card draw. You can't use it for disruption in the way a wheel can. It's just card draw, which is nice, but does make its application much narrower.
I think Boros decks are likely to be the only decks that are really considering both of them. Once you're in Green, Blue and Black, you have better options.
Outside of Osgir who is very well positioned to take advantage of all the cards you've discarded, I think
Secret Rendezvous is a perfectly reasonable shout for most Boros decks. A lot of Boros commanders tend to be combat focused and therefore aren't running an extensive package to recur things from the graveyard, so discarding cards isn't ideal. That said, if your hand is empty, a wheel can be a very efficient way of restocking it, so the chance of you discarding anything important is low.
So, to finish rambling and answer the question, let's suppose:
I'm building a Boros deck. It's not Osgir and isn't inherently interested in the graveyard. I have one slot left that I want to fill with card draw. I have a
Wheel of Fortune (I
wish) and a
Secret Rendezvous sleeved up and ready to slot in. All I'm looking for is refilling my hand. I don't have ways to abuse the wheel by locking out my opponents or punishing them for drawing cards. Which do I choose?
It's honestly closer than I thought it would be, but I still think I'd choose the Wheel.
I do like
Secret Rendezvous in this scenario. 3 cards for 3 mana is a good rate for those decks, and I like the political tool of forming an ally to give the other cards to for mutual benefit later in the game.
That said, I think the disruption I mentioned earlier, plus the fact that you see 4 extra cards, makes Wheel take the slot for me. While not as political, a wheel can still have political ramifications. Either an opponent is happy to wheel, which is usually good for at least 1 "Hey, I gave you seven cards, don't attack me", or they aren't happy with the wheel, which meant the disruption was worth it.
Secret Rendezvous is probably the better choice if you are playing around counter magic or an opponents
Notion Thief, but that's entirely a meta call. As an objective choice, wheel wins for me.
Great question! I really didn't think it would be as close as it was for me. Goes to show what some critical thinking can do for ones opinion on a card.