People being irrational doesn't turn a building good.
OK, I guess you're right and that there are some late game players that haven't tapped into the Dragon Abbey and are still looking for a source of mana. Either way, Storm Phoenix provides more mana.
The Ashen feeding effect is only useful for irrational people, as you say, so this doesn't make it good.
That's understandable and for you they are no good, but that doesn't bring the Ashen up onto a par with them, just because all 3 are no good to you. I too have lots of standard goods. Not your kind of numbers, but most of them up above 5 million. However, as you say, most people aren't like us so those standard goods are probably valuable to the majority.
You also have to factor in the FA crowd. I wouldn't usually waste a pet food on Storm or Aureate in a normal situation, but I'll sink about 20 of them into them in an FA week. Not only that, but Storm Phoenix's feeding effect benefits sentient goods too, so that will often be good for almost everyone, except for people in early chapters and people who are refusing to advance in research.
Just as an aside - You are a spire caterer I think. Both Aureate and Storm are excellent for that in terms of coins. Storm even better because it gives lots of supplies. You are no doubt well catered for in coins and supplies, but extra buildings like these would save you needlessly upgrading your Lighthouse.
If storm and aureates 2 day coin reward has to pull me trough the spire then I am in serious trouble.
Loads of EE and if needed a round of neighbourly help do the just just fine. in most cases the activation round once per week is enough (the round where you help all players to keep them all active for neighbourly help)
5m coins per 2 days is a whopping 1-2 payments in the spire.
Yeah the new FA has revitalised the usefullness from those 2 birds from completely useless to has a use to a very specific crowd, just like the ashen phoenix has a nice market.
If you are short 100 currency and can't spare the diamonds because your not as active in the spire, that ashen phoenix is not looking that bad either

If this was phoenix event 2019 I would have build and used this phoenix every single event. we had no diamond sources, and getting the main prize complete was sort of a gamble already so those few extra event currency could make the difference. I remember I bought the outpost (was a different building but did the same) just to improve my odds. thats how amazing this bird would have been to me 2 years ago.
Since then we are drowning in diamonds but only those that seek them. I went from ~14 premium expansions (bought when the max prize was 10 euro for an expansion) to 37 atm without spending a single penny.
I am able to gather massive amounts of diamonds so today I would not build a building that only gives 130-150 event currency for free, it's a waste of space to me, If i need that 100 currency now I just spend some of my free diamonds instead.
I am betting that that bird that was amazing to me 2 years ago is going to be amazing to many players that are in that stage right now.
Those than can pick up random currency less often and are just making of just not making it every event to a full building.
Many other people are not in the same situation there value on diamonds is totally different.
I am willing to bet you are going to see many many many of these ashen birds in cities. most players do less than 2000 tournament points, they do not want/need a fire bird and this bird will make them more exited than 10 firebirds combined.
You can have a dragon abbey as a late player but without the investment in the tournaments to power it on, it's a lot less usefull.
Just look at your weekly ranking score how many players in the top 100 get more than 5400 points.
You'll be shocked how little that is. 5400 points is 20 provinces so only 40 spells a week.
Try to pay of your 1m+ mana upgrades with that and you see the abbey is a nice addition but cannot be the sole source of mana for most players.
Of course we easily double that, and most likely we also have higher level abbeys I havent had a mana building in my city since the introduction of the abbey years ago.