While it may be irritating that shutdowns happen, such as with extensive gaming, it doesn't indicate something is wrong with the Mac. It only means that the Mac wasn't designed to handle such loads for extensive periods. While you certainly may disagree with Apple's design and the Mac's capabilities, it doesn't mean the Mac is defective. It more likely indicates that you didn't buy a computer best suited to your needs and intended workload.
I don't really game. I have an older mac pro around too. It will be updated once Apple releases a proper update. I only use it for work, even then the 2011 macbook pro is faster at most things. There are no indications anywhere when you buy such a thing that it's not created for X functions. The internal hardware is quite powerful, and Apple advertises it in this way. You can read through all of their spec sheets and policies. Nowhere does it indicate that thermal shutdown is normal behavior
I may repaste several computers at once, and blow out any dust from the inside at the same time. I know enough to be careful with compressed air on fans as it can be stressful on the blades if used incorrectly. I keep everything grounded. I don't walk around while doing this. I'm really quite paranoid with the caution procedures, but I don't work on anything that makes me feel nervous. Typically before disassembling one I'll watch the ifixit videos twice so that I have the entire process memorized 100% down to which direction they pulled which tab.
Most people are not like this. They buy a computer. They expect it to work. The design should be able to monitor itself well enough to prevent the device from having to resort to fail-safe procedures in typical situations. We aren't talking about overclocking or any of that silliness here. We are just talking about anything that can stress out a modern computer in its native clock settings. Ideally the heavy lifting programs would just run slower on laptops than they do on something like a current mac pro. If I experience any problems with my current one, it will either be a clean and repaste or I will take it to a familiar Apple authorized repair center rather than Apple directly. There are a couple that I know, and they're much less annoying than the genius bar.
Anyway I am going to agree to disagree on this one. You provide a lot of excellent reference. I just disagree with you on this point.