Well there is always room for improvement but I don't agree they would not contribute enough as a lot of infrastructure and support just is not labeled defence budget. They even went to Afghanistan after 9-11 no questions asked.
Plus it's clearly in the US interest to have a strong presence in Europe and to remain. The entire problem got blown out of proportion under President Trump for some reason.
I truly miss the strategic view and experts the US had for international politics and diplomacy. Now it's just America first and not much else beyond political correctness and domestic fights. You might have already noticed that China and Russia and others are already trying to exploit this perceived weakness? Much of the problem is caused west of the Atlantic.