BAE Systems along with other European arms/aerospace manufacturers are perfectly capable of making competing products.
They are more battle-tested than any other. America has been involved in a war or another pretty much continuously since the end of WWW2.
Not that they’re going to be allies much longer.
In Syria the US bombs things at their will, same in Somalia. In all Latin America conflicts the US went at it alone.
Maybe pay attention to Greece, Korea, Libya, Kosovo, Serbia, Yemen, Syria (1982), Iran, Iraq (twice), Afghanistan, WW1, WW2
The fact that even as we bicker on this forum British and American forces are in Yemen pretty much says everything.
* correction: since 1776
There's no reason this can't be replicated by other rich nations but it won't be cheap or quick.
I don't see EU countries starting to invade other countries around the globe to test out weapons systems and battlefield tactics. The US on the other hand, kind of did this continuously since WWW2 (to mention recent history).