GreyWord says:
Not just RAW but logically - if your opponent expects a fight - they would also be "ready" for an action. So who goes first if everyone is ready to ? That's the whole purpose of initiative roll and action order based on dice roll.
That totally makes sense, no argument here just thought it was one of those moments where you just go "I guess I have been doing this wrong for a long time"
My IRL DM, basically makes it so the only way to get a surprise attack is a readied action regardless of anything else. Most cases this would be used for setting ambushes, though the method has been used for instances like I was going for as well (basically anti-Surprise).
Reading the arguments for/against this, I do think I am leaning on the side of the RAW side of it. Though, if my IRL DM wants to run it that way, can only help me in that game. Just have to remember it isn't standard operating procedure in most instances