So it depends what you're trying to do. If you goal is simply to deter direct attack against the USA, no, we don't need a military even a quarter of this size.
However, the US has become a sort of 'Global Policeman' in the post WW2 era. A role it could have walked away from at the end of the Cold War but didn't. The US secures shipping routes, it deters aggressive nations from invading other nations (most of the time) and has contributed to worldwide peace and stability. There hasn't been a war between major powers since Vietnam. That's not an accident.
In this security bubble the US has created, a great many nations have grown economically and civically. Without the US deterrence it cannot be doubted that China would have invaded Taiwan and probably several other neighbors. Russia would have simply invaded Ukraine and the baltic region. Not with false flag troops but a true invasion. And the number of smaller conflicts would be much higher.
Global trade has grown immensely in this period and the US benefits from that trade and stability. There's zero question in my mind that on a global scale, the US expenditures are money well spent. Further, the burden on the US isn't that large. US military spending is around 4-5% of GDP most years...sure that's about double most other western nations who tend to be closer to 2%, but it's not THAT onerous in the grand scheme of things.
But the US also has some badly designed entitlements that area eating larger and larger shares of it's federal budget. These chew up around 60% of the budget already and that ratio is expected to grow FAST in coming decades.
So the question really is - is 4-5% of GDP too high a price to pay for the massive global stability functions the US is engaged in? Some say yes, some say no.