And you won't be doing four missions in parallel before you've done one that succeeds and as far as I can see with the known technical limitations an economical improvement isn't going to result in a technical success, just in a cheaper failure.
The tech being there isn't helpful if it's too expensive to use at scale. And the computers then were... passable at best. It would be exceedingly hard to adequately control a rocket for an accurate powered landing at the time.
> you won't be doing four missions in parallel
Well you do have the problem of only having an ideal launch window every 2 years, so you do have to do them at the same time with minimal spacing or wait forever to try again. I think the plan was to only do two ships at a time initially though.
Some things you can compensate and plan for, some failures are just natural or random. Like a micrometeorite hitting two of the main computers or something.
And you won't be doing four missions in parallel before you've done one that succeeds and as far as I can see with the known technical limitations an economical improvement isn't going to result in a technical success, just in a cheaper failure.