If the whole pipeline could be created by a single robot that cost 30 bucks then that would mean that it was a better idea, not a worse one.
Conversely - if the pipeline required the entire population of the US to construct it then it would almost certainly not be worth building.
You make a very good point about how “jobs created” is a poor a measure of the economic merits of a project, such as the pipeline. Indeed, as efficiency goes up (a good thing, in economics terms), the number of workers required to do the task declines. Since the beginning of the industrial revolution, there has been a lot of hand-wringing about automation killing jobs (can you say “Luddite”?); but, we’ve continually adjusted. Meanwhile, our standard of living has risen beyond the wildest imagination of anyone living 200 years ago. It seems that the more we have, the more we want — and that’s kept us busy. Or, more accurately, it’s kept us as busy as we want to be — the work week has dropped by nearly half, in those years. Another good thing.
The talk of “jobs created” won’t go away any time soon. It’s the populist’s way of discussing economic growth. Meanwhile, the best we can do is prevent the other side from getting away with outright lying about the numbers.