Dungeon Descent does not etbt, costs 3 to activate, requires you to have a Legend in play a la Enclave but not tap it as part of the cost, and has no timing restrictions. That would ostensibly put the card on par with Enclave by every visible metric.
That's not quite true since I would say having a legend is a lower bar than having >=4 power. That's the one point in dungeon's favor.
Btw for sake of argument, let's ignore the sorcery-speed restriction and just assume that it's justified because that gets complicated to argue. There's still 3 other nerfs applied to the card that could have been removed (etbt, costing 4, tapping a legend). For the record I still think instant speed would have been fine, but it does allow some things that are tougher to compare to existing effects.
Except I think it would make it much better than enclave. Cards drawn is an excellent ROI for mana spent, but access to options is superior imo. The hypotehtical descent as described above doesn't only draw cards, it does all of the following:
The fact that it could do any of those things is very very far away from getting to simply pick one of those things. Most of the time you'll have 1-2 options at a given time. When you really need a chump blocker, if you're not in the right position to get to one of the rooms that make a token, then it doesn't really matter that theoretically you could get a token eventually.
Given that you only have a choice of 1-2 options most of the time, I'd say it's much closer to randomness than choice. The EV of a choice is better than the best effect, but the EV of a random selection is just the average of that group. It's not exactly random, since you have some control over when and how you move, but in most cases it'll probably be too difficult to predict exactly what you'll need and set it up, especially with such minor effects, so it's kind of effectively random. Plus outside of corner cases, the other 2 non-mad-mage dungeons are probably too crappy to consider. Yes, there's some minor EV gain in the 3% of times you get to kill your opponent at 1, or make a crucial chumper in 2 moves instead of 3, but I don't think that adds up to much and you could basically ignore those two dungeons and only lose a tiny amount of value.
In the vast majority of cases I think the most reasonable course of action is just to beeline for the end rooms of mad mage, and hopefully the junk in the early rooms ends up being worth some fraction of a card. Under that model, the question is "is the value of all 7 rooms of mad mage worth more than 7 cards" and I'm pretty sure the answer is a hard "no". On top of which, it's back-loaded payoff. If you only get to room 4, you've basically spent a bunch of time accomplishing mostly nothing. Drawing cards is good right away, at the beginning of the game when value is more important. Casting a spell for free is great, but if it's not until turn 8 then it's really not THAT exciting.
At the end of the day, this is a matter of opinion combined with mutual inexperience using the Venture mechanic.
I agree that it's hard to be completely certain, but I'm betting that wotc has run the playtests. If venture was > drawing a card, something like triumphant adventurer would be INSANE. Nadaar would be insane. Just imagine a 3/3 for 3 that etb draws a card, draws a card on attack, has vigilance, AND has an anthem upside that he himself enables. That would be beyond bonkers (and in white? wotc would never allow such blasphemy). And if you're right, the real version would be even BETTER. Even something like Bar the Gate
would be a double-upgrade on the powerful Exclude
, a card from back when counterspells were stronger than they are now. Fates' Reversal
would be an upgrade on a bunch of cards. Fly
would be a huge upgrade on Curiosity
(minus the noncombat part, which is important for commander players, but combat-only-curiosities have been standard relevant in the recent past). Yuan-Ti Malison
would be a massive upgrade on Vedalken Heretic
and all the 3-cmc ophidian-alikes. All this in a set that most people agree (yourself included) seems to have a lower power level than sets before it. So you'd have to either think that (1) WotC has badly misjudged how strong this mechanic is, or (2) in a set of otherwise low power, a high percentage of the venture cards are significant power creep on existing, often-already-strong cards. Or, of course, (3) WotC probably got it more-or-less right, venture is weaker than drawing a card, and all these examples are good but not insane cards, in line with the rest of the set.