What if your in-house engineers are morons but you need to have one particular project done correctly. I don't understand the glorification of normal engineers - quite often they're normal people drawn from normal distribution, with all consequences of that.
Why would you hire, and then knowingly continue to employ, morons? Your employees are not chosen at random, you can evaluate their skills and select the ones optimal for your organization, as demonstrated both by their prior experience and their work performance under your employment.
On the other hand, the people you get from the consulting firm, who were not hired with your particular needs in mind, and who are assigned by leaders who are both unfamiliar with what you do and have motivations which may not be perfectly aligned with yours, are normal people drawn essentially at random from a normal distribution. Maybe you don't need to have a particular skillset in house full time, but the person whose job is to do something will always outperform the person whose job is to maximize billable hours.
This is my experience as well. One of my clients tasked me with stuff their average engineers can't do due to many reasons, not only competency. They just had to have this one project working in time.
Personally consultants are just another tool in the mid-hi management toolbox. Just as a workforce on a payroll, this can be used in a good clever way and this can spiral into a shit show real quick.
