The biggest EU defence needs are two: securing oil ingress from the Middle East and securing resource ingress from Africa. Without the US 5th fleet, Iran or any other regional power could shut down oil ingress, pitching the EU into a sizable (-30%) GDP recession. Instability, of which there is plenty in the Middle East, could do the same.
Same for Africa, with the added threat of Chinese competition for the same resources. Without those raw materials (minerals, uranium, some oil and gas) European manufacturing doesn't have a future. Hence the constant French and American interventions to stabilize various African states and their tight relations with their governments.
That state of affairs is because of the Post-WWII order the US constructed via alliances & multilateral organizations, in response to being repeatedly dragged into European wars.
The only reason they are not in need of defence is because the US umbrella still protects them from invasion by foreign powers. If the US were totally uninterested in Europe, Russia would likely make much bolder moves in the region.
It’s not healthy for Europe to be so dependent on the US, as has been proven over the past 4 years.