In fact, in the current situation we have exactly this issue. SLS/Orion is so absurdly expensive that there literally is no money for dual sourcing of moon landers. NASA was forced to select on Starship as the moon lander BECAUSE there isn't enough money.
If you actually read what smart pro-SpaceX analysts and journalist write, you will see that you can dual source literally every part of the architecture.
We already have (or soon will) have 2 ways to go from earth to LEO. If you build on top of that, and you are not forced to spend money on SLS/Orion you have easily enough money for 2 way to get form LEO to the moon.
Starhip is one of those ways, but other ways of doing the same thing could be designed if there was money for it in the budget, but that money isn't there because NASA was forced by uninformed politicians to use this architecture. Why so many people defend an architecture that is the direct result of clueless politicians I will never understand.
There is a reason every other modern NASA program is dual sourced, COTS, CommercialCrew, CLIPS, Lunar resupply, suits, but somehow Artemis isn't. Why might that be ...
Still, my point was primarily that there is a general heavy slant towards SpaceX on this site which, whatever successes, should be tempered.
But even fans of SpaceX agree that dual sourcing is important, it just so happens that the secondary bids are mostly not as good or inspiring. So they are talked about less.
Of the two rockets that resulted from the original COTS program, Falcon 9 and Antares, I think its pretty clear why when talking about those there is a heavy slant towards Falcon 9.
Had NASA not given SpaceX a chance for HR (as Bolten and others in the Obama administration wanted) the US would be reliant on Russia for ISS and that would be a literal disaster right now.
Success in the space industry is slanted towards SpaceX, and that why its the same on this sight.
Neutron is less capable then Falcon 9 and likely lower launch rate as well. Its really not comparable to Starship at al.
I love RocketLab but they are not really playing in the same league as of yet and will not for a many years to come.