Basically, the effect itself in the exact instant is irrelevant to the tier itself. He could make the wishes of humanity come true in many ways and the individual effects aren't that impressive, normal resurrection, mind manipulation/influencing, a few things happening in a certain way, etc. What matters is the way he makes those wishes become true, that is by taking over the very core of reality and putting his distorted view of an idealized truth as the rule that maintains all of existence working.
Think like you could make half of the universe's population die in an instant. You could do that by using basic death manipulation over a very high area, but you could also look at the core of reality that emanates everything that happens and from that core change a few lines of the code of reality with the result being "half of the universe's population died". You could make that be just half of the earth's population to fit more with the range shown directly in Persona 5R.
The point isn't what he did, but how he did it. If he had unlocked low reality manipulation that lets him shape the world into his personal universe, there are many ways of doing that, in fact, many demons have pocket universes of their own and in the right conditions they could overlap with the physical reality and take over it with the right unbalance. What matters is how; it's the fact that he ascended to some of the highest levels of the Qliphoth/Sephiroth in the very sea of souls they all come from and uses that to emanate his distorted view of the world as the sole single reason for everyone by making their deeper desires become true.
