Both are fallacies for different reasons. You can’t claim your cost was a million, because you didn’t shoulder that entire cost for an average legendary task (unless you are the only one donating to legendary tasks ever in amounts above your guilds minimum). You can’t claim your reward was what you would get if everyone in the guild donated 1 million, because guilds do not donate evenly and rewards are non-transferable. Also, I think you meant Arcanes here, since Runics can’t appear on table 3, and the other two are clearly table 1/2 values.
In terms of a legendary tasks median “value”, a huge amount of it comes from the approximately 1 in 200 chance at giving a random mythic. This means they have less inherent “value” to a given person the more mythics they collect, since they have less and less chance of getting a relevant (new) one. Every rewards system in the game is designed with several diminishing returns gates, so this should come as no surprise. I did the math on the average “value” here: Instead of LTs what about - #42 by Mithran
What I will agree with is that they are somewhat of a joke taken individually, given how extreme the value swings can be. The rewards table should be much more “even” across the board so it feels less like buying a lottery ticket that might give you something you want, or it might give you a small amount of a different lottery ticket that might get you a reward that you actually want, or it might give you a bunch of stuff you don’t want or need. The extreme reduction of table 1 and table 2 values while slightly increasing table 3s made it so that it is uncommon to see something both relevant and in not-insignificant quantities at the same time. I think legendary tasks would be a lot more attractive to people just breaking into them if the reward scheme were a bit “flatter”, so it was more likely that you got something relevant and in not completely insignificant quantities. It is really hard to get excited over a “good” table 3 draw of 8 gem keys or 50 glory keys when you know that doesn’t really amount to anything, or even straight drawing a legendary from a new kingdom that everybody in your guild just got because they saved at least some event keys, or a mythic that is a duplicate (even worse if it is one of the “bad” ones, or even one of the “must have” ones and several people in your guild just finished crafting it).