Huh?! What is the correlation between able to assemble their scuba great to being competent divers in the water? I've seen non-certified salespeople very competently put together scuba gear in a shop, and way more often, I've had very experienced dive guides botch setting up my dive gear on a dive boat (because guests were told not to put their dive gear together). For many vacation divers, the first time they see the dive gear they will be using is right before they gear up, since lots of vacation divers either don't have their own gear, or don't travel with it, or in some cases, the airline somehow lost their bags with dive gear. My wife would be hard pressed to put her own dive gear together, and has absolutely no desire to remember how to, but she's an extremely competent diver, and that's part of the price I pay for having her dive with me
There is nothing wrong with being a vacation dive and enjoying the dive if you're a competent and safe diver. In many cases, these type of divers significantly improve diving for me, because halfway through my dive they're all out of air and on their way to the surface, so the guide and I (and my wife) essentially get the second half of the dive with the guide all to ourselves to find interesting critters without everyone bumping in to us