I get that, but then what was the point of the video in this discussion? They didn't have the part available. If they don't have the part they can't fix the machine. That doesn't really have anything to do with the difficulty of fixing it. Sure techs make mistakes, no one is perfect, but you don't build that into the cost of replacing a hard drive.
I guess you didn't really get the point of the video. The point is that, no technician will want to practice how to open this iMac, knowing that one mistake makes them liable for their customer's brand new machine, because you can't even get the parts to fix it! The difference between iFixIt and an Apple authorized repair shop is that, iFixit bought their own machines to take them apart. They are not liable for any damage other than themselves! And their technicians have many opportunities to practice on those machines, so obviously they are going to get really good at fixing things.
In the good old days of repairs of most electronics equipment, it is "DURING" the warranty period that all the technicians who hadn't been trained and gotten the experience would have had that 1 to 3 years warranty grace period, where the manufacturer would eat up the cost of the damaged parts, knowing that the techs are in the learning period. Certainly, when some techs are causing more damage than the average norm, then those technicians will be recalled, re-trained and re-certified. And if there are too many mistakes made, then those techs will loose certification. But the bottom line is that, the manufacturer would eat the cost of the damaged parts under warranty repair, because manufacturers then understood that maintaining good customer service was ultra important. That was then. Today, it is the technician or the shop who is NOW liable for any damaged non-defective part repaired under warranty. So if you damaged the screen or the logic board when you first work on the computer, the liability is on the tech and shop. Some shops would take on this liability and eat the cost simply because, it is the cost of doing business. But today, parts costs are just obscenely high (no thanks to Apple Inc -- please view chapter 2 and 3 of the video) that you are better off buying a new computer than fixing it under warranty. Which is why you hear this so common that when your Mac fails, there's a high chance that you are going to be buying a new Mac. Older Macs are somewhat repairable, whereas newer Macs are increasingly more difficult to repair.
So basically, it is Apple's policy to ensure that no used parts are sold on the internet that is causing this lack of technician experience. So yes, you can say that the OP should not be paying for the technician's training or mistakes. But it's not that tech's fault. It is Apple and Apple's drive to not allow third party shops to repair their products. So if you don't allow someone to repair your product by making that someone fully liable for his/her mistakes and no parts support, how then can that someone gain the experience to open up the iMac or even bother when the odds are stacked against the third party tech?!? Somehow Apple expects the techs to spiritually beam this experience without taking apart a single iMac. This was the main theme of the video. It is Apple's attempt to stop people from fixing their computer. Some people use iFixit as always an excuse that these techs should know better. iFixit buys their computers to be dismantled. The techs in the independent shops don't and how fair is it for the tech, who is only earning slightly above minimum wage, has to shoulder the complete burden of the total replacement costs mandated by Apple if they make a mistake? Best insurance policy; charge the customer for the potential damage that it may incur. The OP and the tech at the shop has at best a 50/50 chance of not breaking the screen. An experienced iFixit tech would have a far better odds of not breaking the screen, but that is not an iFixit tech the OP is getting.