A rebuttal to your arguments against Mana Crypt: it costs 0 mana. That means you don't have to play it T1. If you have a sweet 4 mana play that will have a large presence on the board (say, Teferi, Master of Time), just hold it in hand until T2. You don't pull aggression from other players until you would anyway (in this case, from Teferi, Master of Time) and you don't start losing coin flips early. As for Mana Vault, it lets me play a 5 drop T2, and Vault with any T1 ramp that can immediately tap for mana can give you a 6 drop T2. If Sol Ring + Mana Vault lets me win the game on T2, then that is pretty good ramp. Having to pay to untap doesn't matter at all when there are so many ways to untap it for free.

Also, once you start bringing in personal experience, arguments kind of lose all meaning. I play a lot of mono or dual coloured decks, and I run Maze of Ith in pretty much all of them (also a respectable amount of artifact and land wipes). Unless your creature has hexproof and pro my colours, it will never connect. Between board wipes and spot removal, you would be better off playing Llanowar Elves, since you can run so many effective copies of it (eg, Elvish Mystic, Birds of Paradise, etc).

Also also, one of your stated rules is "Creature cards needing to attack". Does a Sword not break that rule, since it requires a creature to both attack and connect? At least Sword of the Animist just needs the attack trigger.

My personal opinion is that the most impactful plays are 4-6 mana. Being able to reach 4 mana on T2 and 6 mana on T3 should be a qualifier for "Most Optimum Ramp". I would rename this list to "Useful Ramp Cards". I do think this is a useful list, but I don't think it is a list of the best ramp, which the title claims it is.

About your last point, could you share that research?

Magical Hacker I don't think potential opponent aggression is a valid argument against Mana Crypt. If you don't have a follow-up play for it turn 1, you can just wait to play it until you are going to use the mana for something. If you play it turn 2, is it more threatening than a turn 1 Sol Ring? Does it draw aggression more than a Gaea's Cradle, the power of which is directly to your board state?

Magical Hacker Also, what about Seedborn Muse? If games take 10.29 turns, we play Seedborn Muse on turn 5, and there are 1.32 boardwipes per game (stat also from thar Commandzone episode), that's looking at ((10.29-5)÷1.32) turns Seedborn Muse is still on the board, producing a minimum of 5 mana per turn. That's an average of 15+ mana advantage.

Shoot, my math is wrong in the previous comment. Disregard!

Burnished Hart is 6 total mana for 2 lands. This does not meet your first requirement. Golden Guardian also costs 6 total to flip into a 2 mana producing land.

Regardless of aggro and percentage of life lost, Mana Crypt produces 2 mana a turn for 1.5 life. That's better than your 1 life per mana cutoff.

Been tussling with a Boros list, and the curious conundrum of Fires of Invention. It's very much like a Red Sorcery version of Wilderness Reclamation. Cast Fires off four lands, immediately follow up with another 4-drop spell. As later turns go on and both spells in a turn use no mana, this also frees up mana for various activated abilities.