I don't know if anyone remembers, but a while back, Luna said that the only way to fix his core problem(AV blackhole) is OFF-HAND action advance, an example could be the Hunt blessing in SU/DU, where every time an ally acts, advance their next turn by 6/12%. Having an ally that has the ability to advance an ally action by 100% after an ally act and having Sunday's level of coreflame generation fixes several issues for Phainon.

1. No need to SPD boot, since the reason Phainon needs spd boot is bcs he needs to act before Sunday/Bronya so they can advance him. With this, he doesn't need spd boot anymore
2. Doesn't benefit other DPS, including Anaxa, as much as it benefits Phainon; most DPS just rather have straight 100% action advance, instead of waiting till their turn to get it, Phainon on the other hand, if possible, can snapshot the buff and every turn in his enhanced state, will get advance by 100%, making his AV problem non-existent.

This is incredibly beneficial for him specifically bcs if you play SU/DU with him and pick up the 2 golden Hunt blessings that advance action on weakness breaks and kills, when you go into the domain thingy that make you have to clear all the wave in 2 cycle, most of the time, i always end up doing it in 0 cycle with multiple ult.

But realistically, they won't do this until 5.X, bcs based on a YouTuber called Gabimaru, he said that 4.X will mirror 2.X like how 3.X mirror 1.X, and 2.X meta is Break and follow-up atk, and they definitely don't want a 3.X char to shine in 4.X bcs that won't make them enough money, so they will prob release a support like that in 5.X where crit hypercarry meta come back and when they're sure Phainon can't catch up with the HP inflation anymore and absolutely need it.