Apollo was ridiculously expensive. it was a proof of concept, but not sustainable for long term exploration

You would be the first person to ever accuse the Orion program of cutting costs.

Engineering is done in the context of constraints, cost is one constraint - and its a relatively conserved constraint. Saving labor in one area allows for more care in other areas. Especially given that labor is often not cost constrained, but skill constrained, which is less elastic.

The fix for not doing that by hand is to get a robot to do it, given the applicator is human-held, a human-strength Kuka with enough reach to cover the area it can handle before the applicator needs refurbishment of some sort which would give a good opportunity to move the robot to a new section of the heat shield.

For the Apollo spacecrafts:

> The paste-like material was gunned into each of the 330,000 cells of the fiberglass honeycomb individually, a process taking about six months. [1]

[1] https://en.wikipedia.org/wiki/AVCOAT#Apollo_Command_Module

Labor intensive methods aren't automatically better: you have more manual steps which must be done perfectly and validated etc.

Thats what engineering is. If you dont have to consider cost or labor, a lot of engineering becomes much easier.