If we were going to do what you suggest, then we should just boost ISS's orbit and refurbish it for that purpose. We could probably use its current orbit as an assembly point now but there might be too much atmospheric drag to be optimal. A ship assembled there would probably still require significant fuel to leave earth's orbit. But ISS also has a number of cranes and robotic arms that could be used for assembly. Such a terrible waste to de-orbit an asset like that.

There are a slew of new space stations launching in the next few years that might also fit the bill eventually for what you suggest. I really don't know if any of them will have the capability. A space station for assembly of large outbound spacecraft is an excellent idea and a worthy endeavor for sure. I'm certain it will happen eventually.

But waiting for that now adds another step in the process that will delay the initial moon base plans by years or decades. Space ship assembly stations in LEO will be a must for exploration long term. But if we can launch directly there now and start building a moon base, let's do it.

If the Moon Base User Guide were simply a marketing brochure I don't think it would have listed so many problems we need to overcome in order to build a moonbase. It makes it seem almost impossibly difficult it is fraught with so many gaps in knowledge and technology we need to close. Did you really give it an honest open minded read?

The current plan to have 73 launches, most of which are unmanned, will preposition tons of hardware and supplies for our astronauts. They expect failures along the way. But we have put landers and rovers on multiple planets already vastly farther away than the moon. It's not beyond our abilities to get assets up there.

As for the next manned steps, Artemis 3 is an LEO test of refueling in space and testing the lander. Artemis 4 lands on the moon. Artemis 5 lands and begins building the permanent base. Will these planned launches slip? Very likely. Meantime, a huge amount of private sector activity will be taking place in LEO. IMO, no reason both your space station idea and the direct flights can't proceed at the same time? Eventually, the former will support the latter.

After Artemis 5, SLS is done. If all goes well Starship and/or New Glenn will begin a much faster and cheaper launch cadence. Call me an optimist if you like, and I'll try not to call you a cynic.