Designing something that can be built efficiently, and repaired, is also part of engineering. As is something that can cross a bridge, and move at a respectable rate. It’s all part of engineering, so is a reasonable price. There’s always tradeoffs.

You are, indeed, wrong. Designed by Bantam (who made trailers for them) in about 80 days for the trials, and built by Ford and Willies Overland. The War Department didn’t think Bantam big enough to do the job, as usual in those days, they were right.