Except the idea of "later in the round" doesn't actually exist, all of these actions are supposed to be happening simultaneously, the creatures and characters in combat aren't actually waiting to take their turns, the whole "turn order" is simply a necessary abstraction to keep play from becoming too confusing. In fact, you can't "delay" in 5e rules to act later in the turn even if you wanted to- if my Cleric's initiative count is 20, he can't choose to do nothing on the off chance someone gets hurt later in the round for him to heal. He'll have to wait til his initiative count on the next turn to do that.
Ready doesn't even change your initiative count, it simply allows you to try and be more precise with how your action flows with other actions, but it comes with a cost.
-It's worth noting that this should also be the "aha" moment for understanding why you shouldn't be allowed to take the Magic action for a leveled spell when it's not your turn if you also used a Magic action on your turn to do the same, since it's all happening in the same 6-second combat round. Unfortunately, WotC decided to allow shenanigans like Sneak Attack when it's not your turn, which leads to debates like this (I realize there was pressure from players about this, but they really should have stuck to their guns about the narrative flow of the combat round).