Or the +25 rewards are 421 (+3ilvl in M+)The change to M+ and even raid loot overall was pretty meaningful and does add a feeling of progression back to the game that was previously only felt in mythic raiding. Doing 25s for end boss Mythic raid ilvl would make it even crazier but adds massive loot balancing issues since you can then get every M+ dungeon loot table+any tier slot at 424 ilvl where as from raid you only have 2 bosses worth of loot tables at that ilvl. No one can really do 25s yet but when they become more realistic when everyone is 420+ ilvl mythic raiders would basically be forced into them for loot optimization.
Ideal situation imo would be just splitting raid in half, early mythic ilvl and then late mythic ilvl. Then have 16s reward early mythic ilvl vault as they currently do, have 22s reward late mythic ilvl vault and have 19s reward halfway between them.