If they get less performance or more mission payload, they can add tanker launches. If they get more performance or less mission payload, they can remove tanker launches.
People ran into "the design is 10% heavier than planned for unexpected engineering reasons and now we have to make hard choices" on space missions far less complex than a literal Moon landing. SpaceX has externalized the "hard choices" into the tanker count, pre-emptively.
The lunar orbit of Artemis is defined mainly by SLS/Orion's performance, or lack of thereof. The specific NRHO was a Gateway choice, and might now be dead alongside it, but by itself, Orion can't get to low Lunar orbit. Which drives some peculiar design choices.
So many (perceived) problems with spaceflight and building moon bases and the like are solved by simply making the process and cost of launching faster, easier and cheaper; the problem that NASA has always had is that each launch, even with the reusable space shuttles, cost billions and took years of engineering, planning, etc. To the point where yesterday's launch was done with (what I perceive to be) salvaged parts where the engineering was done decades ago, because engineering something new would be too expensive and take too long.
Sure, don't fix what isn't broken and all - *nix tools are decades old too after all - but still.
If they get less performance or more mission payload, they can add tanker launches. If they get more performance or less mission payload, they can remove tanker launches.
People ran into "the design is 10% heavier than planned for unexpected engineering reasons and now we have to make hard choices" on space missions far less complex than a literal Moon landing. SpaceX has externalized the "hard choices" into the tanker count, pre-emptively.
The lunar orbit of Artemis is defined mainly by SLS/Orion's performance, or lack of thereof. The specific NRHO was a Gateway choice, and might now be dead alongside it, but by itself, Orion can't get to low Lunar orbit. Which drives some peculiar design choices.