I don't think it is as clear cut as - not at their level yet=cant go toe to toe. It is of course down to the type of manager you have and how he decides to go about things.
For me it's like when Trappatoni was with Ireland. I personally wasn't bothered complaining too much about the details of the horrific football on display because basically we got what we paid for with him.
Koeman is what he is. He seems he would be more cautious than gung ho and that's what we paid for, but that doesn't mean that another manager being more positive can not achieve results in these big games just because the squads worth less, its their first season or whatever other reasons given.
In these bigger games next season, I am hopeful we will see more ambition and a noticeable shift in the psychology of the squad in how they handle them....or handle any big moments that come our way. However, I am more inclined to think he will stay more or less the same.
We will see!
In fairness, Koeman was 30 seconds and a moment of panic away from being the first the first manager in Premier League history to win three consecutive away games at Old Trafford.