On paper both the EU and US have a massive industrial base, even the car companies alone have enough expertise, workforce and equipment between them to quickly pivot to military production.
Politically that won't happen because they are not at war with Russia and cannot simply commandeer civilian enterprise for military use. Furthermore even if they did, with the complexity of modern military equipment by the time they actually rolling out tanks and missiles for Ukraine it'll probably be too late.
What they CAN do is empty out decades of warehouseed equipment then increase their military budget for the next 10 years to refill the stockpile, which some EU states are already doing.
Politics has very little to do with it, it's all economics.
If you aren't trying to build new capacity, then the issue is Just-in-Time/Lean manufacturing means there is no excess workforce or production capacity.
If you use GM's workers, every Javelin made by them, is one less car. How do you expect them to make money?
They won't sacrifice a customer since they have a great opportunity with their EV production ramping up ahead of the Japanese competition.
Has nothing to do with complexity. You have computer aided design, you know what equipment you have on hand. You don't have to make Bradleys or M1s. Rather, you might quickly push through a new design that you know the equipment can handle like an MRAP/APC based on the GMC TopKick (like the presidential limo which GM already made). It even has a hardened DuraMax Diesel.
The problem with your other suggestion is that the conflict is clearing out even the warehoused equipment. Sending out things like 105mm howitzers, Aspide, iHAWK, those haven't been state of the art for decades. Aspide was able to be built by 90's China and even the PLA quickly moved on. For all the laughing at Russia sending T-62s, it's hard to not draw the parallel here.
