Nobody ever is. You’re forced into it by external events, and you either kinda make it work, or don’t. It was, after all, changing times and dumb moves by a mad despot that caused the US to revolt and form a country.
The US makes up approximately 15% of NATO funding and I don't think the EU is in an economic position to make that up any time soon. NATO is arguably underfunded as is.
I'm not so sure - everyone goes on about the EU's relative lack of GDP growth as though it's a death sentence, which is obvious hyperbole.
In any case, numerically I'd imagine that 15% being made up by spending increasing by 2-3 times by the remaining 85% (from 2% previous target to 5%, or 3.5% more realistically).