A few years ago, I volunteered in SE Asia for 18 months using my electrical engineering skills to help rural villages get access to electricity. At the time, I'd been working professionally for around 7 years and was just becoming competent at working independently. Although I'd gotten my PE status a year earlier, I can't say that I was at a senior engineering / consultant level.
So it was a surprise for me to find that I was one of the most experienced and skilled engineers in my organization (and in many other energy-related organizations for that matter). I concur with the OP and have met quite a few western volunteers that were well-intentioned, but generally had no technical skills.
Of those who had qualifications, they were usually in the social sciences, development studies, media / communications, public relations, etc. Useful skills no doubt, but I felt that the country could have benefited more with direct assistance from the hard sciences and engineering, e.g. hydrology, agriculture, civil engineers, etc - those skills were always in demand. In the end, there's a reason why development is often done so badly - they practically let anyone do it.