I think it's completely fine for Persona 5 Royal's influence to seep into the remakes of Persona 3 and 4 provided we're all willing to admit that's the case because the battle system from Royal clearly were retooled and reused for Reload and Revival
There's a meme going around Twitter right now of Persona 5 Royal next to the three remakes that all came after it that's trying to highlight how distinct and NOT like P5 they are and it really just has the same energy as these being four different The Rock movies.