Disclaimer: I might be one of those "crazy tourney players", with ~3.6K every week. I don't even think it is particularly difficult to accomplish, nothing extreme here
Having said that, I think anyone who does even a bit of tourney (and you should, at least for those juicy KPs) benefits a lot from max Fire phoenix. In fact, I think this phoenix is much better compared to the other ones. Higher pop than other phoenixes? Check. Having the best (i.e. most difficult to obtain by other means) maxed out reward? Check (Portal Profits). I mean, boosted T1 goods for Aureate phoenix? Come on now
Also, I think concept of phoenixes works much better for the Fire one. Goods productions is all about sustained rate of production, not bursts. You can't run your manufacturing in permanent boost mode (OK, some people do, almost). The boost that goods phoenixes provide is just too short, at 3.5 hours! I don't think you can setup sustained production of pet food to several a day.
But Fire phoenix only needs 3 pet foods a week, if you do it right. There are 6 tournament stages 16 hours apart, and pet food boosts for 24 hours. So each boost can cover 2 stages! 3 spells a week is more than doable.
And you can get up to 50% damage bonus! And it applies to all the unit types!! This is super powerful. There are several AWs that cover damage boost for different unit types, but they all top out at 40% at L30. Fire phoenix L10 gives you 50% for all units! And can you imagine space and KP requirements for several L30 AWs?
I can't wait to get it going. Martial Monastery + Fire Phoenix would crush all tournaments!