to defeat the russians?
Seems all they have is their nuclear weapons. The entire western world wants no part of a nuclear exchange with Russia.
so is all this conventional military really kind of unnecessary?
The problem with this topic is that it's a complicated one, made of many different topics, weapon systems, views of policies, but it's heard to remember one public discussion of it ever that dealt with much of any of that instead just treating it all as one thing, the two sides of the argument being you either want to make America defenseless or you want to spend unlimited amounts.
For example. One topic is foreign bases, but even that topic is made of many topics. The issues with a base in Okinawa are not the same as for a base in Poland. There are issues with troop compensation and benefits, VETERAN benefits - think of all the VA controversies. Issues with conventional responses versus nuclear, issues with what we should do on chemical and biological weapons to prepare for risks from others.
Especially important are systemic issues with the Pentagon, where military companies with many billions of dollars at stake have aggressively set things up to manipulate the government to serve them and not the people - setting up jobs in every state and every key district and as many as possible, jobs that can be used as a political threat if the Congress person doesn't vote how the companies want, and essentially a takeover of the Pentagon where senior officers who decide on weapon system purchase recommendations are co-opted, themselves with the 'revolving door' where after 'good service' for the companies they can retire to become a well-paid employee of a company, but where the officials protect that system by ensuring anyone promoted to senior positions is 'on the team' and will 'play ball' with the system rather than challenge it - I suspect.
I could tell a first-hand story of an example of seeing this happen, where there was a military project run by an officer for years, which was 'really' operationally run by contractors for their benefit - and after some years of this the officer in charge retired from the military, I heard, to work for that contractor. I saw a case firsthand where profits were protected in this project.
My point is, there are a thousand specific to discuss - how is it decided how many ships we need versus how many aircraft versus how many other systems and weapons, for which parts of the world, where do things like being prepared to be able to give Ukraine many weapons quickly fit in? It's an enormous topic, but only gets discussed in 'you want the US to be conquered' or you don't.
My short answer is, yes, we greatly overspend.
But when there are cuts - if there were, hypothetically - where do you think they'd come from in this corrupted system where spending priorities are set by the companies? Probably in ways to cause the most political damage to those calling for cuts. Let's cut spending on the troops, angering the public to create a backlash against the cuts... let's cut a popular system that the public is angered by and makes the public feel unsafe.