I will have an unconventional response to this. Russian invasion is used to argue we spent to little. However NATO profoundly outspend Russia already hand Russia has proven utterly incapable of winning a war against a country with minuscule military budget compared to NATO. The Russian military has exposed itself a a paper tiger.
Quite the contrary it may be argued that we are spending far too much on defense. Our spending does not reflect the fact that Russia is far weaker in military terms than we had expected.
Rather than spending more I would have liked to see money spent better. A lot of weapon systems have shown themselves as rather useless.
We should get far more drones and anti-tank weapons.
Russians love artillery and we should focus on weapon systems which can effectively take out artillery.
We also need to upgrade things like bomb shelters, and better secure electric grid, communications and water supply against invasion.
I don’t necessarily think the most modern and fancy equipment is needed. You see in this war how good training, coordination etc is alpha omega. A well coordinated and trained military will pack a heavy punch.
Maybe fancy tanks and fighter jets are less important.