I don't mean to pinch the bubble you're blowing, but, like Azunai before you, isn't this raw data taken in a vacuum presented as practical fact?
I gave my opinion. If yours is different, then that's fine. I personally don't feel that Potential is worthwhile on its own, and think that generally speaking you get more from having a real trait than from having the +1 accuracy/spell resistance/spell mastery and +2 health a fraction of a level early. I consider this to be true for Warriors, Defenders, Commanders, and probably Assassins, but on Mages I tend to take both Knowledge and Potential since I generally prefer direct-combat mages, and they tend to have a lot of level-dependent spells.
I also only gave my opinion at the end of the post, rather than mixing it in with the data. You can draw whatever conclusions you want to from the data I gave, and it should be relatively easy to take what I gave and separate it from my opinion (which, I might add, is intended 'as a general rule', but not as an absolute). There are situations where taking the experience-boosting traits might be more reasonable than others, and there are situations where they are not useful. I tend to feel that Warrior/Defender/Assassin champions get more out of their class traits than from levels, so unless I'm planning for a long game I probably won't take Potential on that type of champion. The data is there if you want to supplement your gameplay experience with something less anecdotal, and if you want to take it and theorize without reference to the game, go ahead. The opinion I gave is based off of my gameplay experience (I've done things both ways at various times - taking all the experience-boosters as soon as possible, and taking none of them, and sometimes taking one somewhat later in the game), and the data I have seems to support my experiences. If your experiences differ, that could be an effect of your playstyle, or your preferred game settings, or any number of other things.
Now, my rationale:
Thus the problem isn't the flat exp gain one gains through these traits but the snowball effect of what faster exp means in a game based around levels = power
The faster leveling is only marginally faster. You can approximate how many fractions of a level ahead you are essentially by a linear interpolation between the points I gave. Compared with a champion of level x who has no experience boosts, a champion with Potential would be about 0.05*x levels ahead, and a champion with Knowledge would be about 0.08*x levels ahead.
Moreover, most of what champions get out of gaining a level is the trait that they pick. Thus, picking Potential instead of, for example, Lethal is sacrificing power now for the promise of power later, and some of the traits you are putting off for later could be a rather significant amount of immediate power (for example, if your champion has an attack rating of 10, and you have the option of picking a trait for +3 attack, that represents a roughly 40% increase in the damage that champion can do; Potential will not match this until you get to be at least one full level ahead, because until then you don't have any more traits with direct benefits than you'd normally have, and the basic level bonuses are generally insignificant compared to the trait bonuses on champions).
Beyond that, most of the higher-end bonuses aren't really as much of an advantage as you might think - in the early game, when your attack rating is 10, +3 attack is great, as it then represents a bonus of about 40% to the damage you deal per hit; later on, when your attack rating is up around 20 or 30, this only represents a damage bonus of 10-15%. Evoker IV isn't as good as you might think it is - +20% spell damage sounds great, but this is applied to the base damage of the spell, so when you compare a mage with Evoker III and a mage with Evoker IV who have equal numbers of shards, the Evoker IV mage is only doing about 12.5% more damage than the Evoker III mage, if the spell damage is independent of level. If you have the need for spell mastery, then each Prodigy trait is equal to five levels (or more, if the bonus is more than +5 spell mastery - I don't remember if that's the correct bonus for Prodigy), and at 1 spell resistance per level the extra level you might have doesn't counteract it, though I will say that spell resistance and spell mastery have rarely been a significant problem for me. The same argument applies for the spell resistance traits available to defenders; +1 accuracy being a level ahead let you go from (for example) an 80% chance to hit something to an 81% chance to hit something, so since level generally doesn't have anything to do with your attack rating the damage your non-spellcasting champions deal is essentially independent of their level, and +2 health is mostly useful for low-level champions, particularly before large units of trained troops or monsters start to become common opponents. About the only time levels, independent of traits, grant power for champions is when you primarily use something that does level-dependent damage (certain spells, a handful of rare weapons) or when you have something that grants a decent per-level bonus (e.g. a shield that grants +1 defense per level).
The Commander-line trait that lets all of your units move immediately is just about the only high-level trait I can think of that is really impressive compared to what a champion just one level off from having it can do, and you could have that by level 10 if you wanted to, or level 11 if you took Potential - but you get your basic champion up to level 10 on less unmodified experience than it takes to get the Potential champion to level 11. Only if you're taking it at some point past level 20 will your Potential champion have earned less unmodified experience than your basic champion in order to get to it, and since in my experience most of my champions more or less stop leveling somewhere between levels 10 and 15, if there's a trait deep in the tree that I want, this means that Potential on its own is never useful to me, since to have the same number of power-granting traits I have to have at least one extra level compared to non-Potential champions, and this is never cheaper for the Potential champion in terms of base experience than the preceding level until you're up to level 20. For Knowledge, this break comes in around level 12, and for Knowledge and Potential, this comes in around level 9 (but unfortunately, with Knowledge and Potential you've sacrificed two power-granting traits, which shifts the less-base-experience-for-same-number-of-power-granting-traits point up to level 18 on the non-Potential champion).
This is my rationale for why I think Potential, on its own, is only particularly useful for long games where you want champions to reach high levels. If you have additional experience boosters to tack on to Potential (e.g., a +10% bonus that lets you consider Potential on a non-mage to be equivalent to Knowledge on a mage who lacks that extra +10%), then it could be a different story, depending on what exactly you need out of your champions.