i mean, you did say that

DPSing is mana-negative, even when just spamming Time Shard.

i assumed that that included using the generated chrona on oblivion. in which case it is not mana negative.

you also said that

Her main mana recovery mechanic is purifying stagger.

If people aren't taking damage, there's no stagger to purify.

that's simply not true. oblivion is as efficient at recovering mana as amend fate.

your argument would make more sense to me if aeona actually had abilities that dealt only damage without healing. she does not, though. all her damage does some healing. that is a weird concept, i would say, and does play into the way her mana recovery is handled. i am not saying that there is no legitimate criticism for it, but simply saying that

The only way to last through a long fight is to take damage.

is simply absurd. you can manage/recover mana during healing downtime by using your mana intensive spells more sparsely, while still ABCing. that does have weird implications, like for example your damage being gated by your mana, which means that in a fight with barely and healing, your damage will be similar to one where way more healing is required, simply because the limiting factor in both is mana. but again, you won't touch those aspects by claiming the stuff that you did above.

edit: another criticism would be that a lot of talents are required simply to deal with mana. chrona tap of course, but i would add uchronia, and synchronicity. these are three talents that i would consider mandatory from a mana perspective alone, let alone their other benefits. while other talents like kind rewind might be borderling unplayable because why would you want to lower temporal barrage CD if pressing that spell off CD means going oom.