You are 100% right, you do not have to accept it or be party to it.
Xometry's response time is typically terrible, I can agree to that! I don't see very many 2 day lead time jobs, I typically see 3-4 weeks, are there shorter lead times, yes, with terrible pricing, of course there is.
I don't take very many low paying jobs, so a $600 job I would more than likely pass on it, occasionally I do, when I'm bored and have an open machine and my other machine has a long cycle time, and if I have material and tooling in stock I may grab a few jobs under $600 that I can bang out in a day, cause to me if my second machine is sitting and my other has a 3-4 hour cycle time and I can bang out 2-3 $4-500 jobs in a day, that's an easy $1500.
I wasn't necessarily referring to your exact $600 job, it was more of a in general comparison to shops stocking certain tools that a lot don't and/or having a lot of a specific tools some don't. Another example would be insert tools, I have just about every insert tool from tangless and tanged along with every STI thread gage, including Keensert install tools, if someone was to take a job with multiple, they get expensive real fast, I've had jobs that require 6 different insert sizes, the insert tools alone would come close to $1000 now add in STI thread gages you could be pushing $1500-2000 fast for one job.
I don't know about different tolerances, I've never come across that. But there's a tier system, I've heard things are different for newer Partners in recent years, could be a major factor. But there are a lot of large medical and aerospace companies that run tier systems no different, when you first become a vendor you are at the bottom, you need to prove your shop and capabilities. No company wants to give a random shop a $20k PO to find out 1-2 weeks later they can't even accomplish the job, need to prove what you are capable of, any shop can have the capability but doesn't mean they have the experience.
I acquired a new customer, locally, last December. First meeting they told me, the first few months I would get the bottom of the barrel work, with short lead times and low paying but after so many jobs of proving my capabilities, quality and being able to hit due dates I would move up tiers, in about 45 days they quit having me quote work all together and started sending me PO's with $0 and pre determined due dates, with the understanding I would bill T&M and they would cover any expediting cost, and they informed if I took advantage of it I would go back to quoting jobs and competing against other shops that are quoting.
Also people need to realize, not every machine shop has the same overhead, not every shop needs to clear $150-200/hr, or whatever it may be. I am a home shop with a VF2SS, VF3SS, EC400PP and SL20, I have very little overhead and can be very competitive if needed. If I became desperate for work, I could easily quote at $50-75/hr and be perfectly well off.