I have a slightly different take on that: the people buying Macs with lower specifications probably aren't the enthusiasts who use this web forum, and if they have any hardware problems they'd probably go straight to Apple without posting about it. Most people buying Macs with higher specifications are plugged into communities and will share their experiences.
Apple has the data on returns and warranty hits. They won't do well if their higher-end machines are regarded as untrustworthy, and if the enthusiasts start trashing them widely. People accuse Apple of not exerting the same level of attention to detail as when Steve Jobs was in charge, but whether you believe that or not it's very difficult to believe that they're not carefully ensuring that higher-end upgrade options can't be used reliably.
45˚C isn't a higher temperature for the sensor. My Mac is earlier and tends to idle in the upper 40's; under load I go into the 60's (I'm living in the tropics). People say that heat kills electronics, and to a certain degree that's true. But modern systems have various failsafes to ensure that they don't go into dangerous temperatures for the components.
As long as you're not riding the upper end of normal all the time, the temperature alone probably isn't a concern. A few years ago I read about thermal stress on components - that is, how being cycled from room temperature to high operating temperatures in a short amount of time causes more stress on components than operating consistently at a higher (but within tolerance) temperature. It makes sense; you hear about similar concerns in caring for your kitchen cookware and utensils. Yet even that is something that has an impact in the long run. I only bring it up because it's interesting to me that people worry about the temperature alone, yet people regularly are subjecting their systems to thermal cycling stresses and don't even think about it.
Are there widespread reports of failure with this computer? I haven't heard of them, but you could check that. Do you live in one of the hotter parts of the world, and have you had other computers fail due to heat issues? You have a winter, so I'm guessing that you do not, and it sounds like this is the first failure you've experienced so I'd guess heat isn't killing things for you left and right. Are there things you can do to help ease your concerns - perhaps moving your computer so that it isn't in direct sunlight, or ensuring that it has good airflow? Go ahead and do that.
No rumors at this point, and it's unknown what Apple will do with the iMac Pro. The new Mac Pro is coming out this autumn, so the suspicion is that Apple won't do anything with the iMac Pro for at least the next six months so as not to draw attention and sales away from the Mac Pro.
Hardware failures happen, no matter how careful you try to be and no matter which company you go with. I've had two MacBook Pros that had faulty graphics chips (the big, bad faulty ones where Apple issues an extension of warranty support for failures related to that issue even if people don't have AppleCare in effect anymore. It was inconvenient to not have my computer for the few days it took to repair them, but it was all done at no cost. It's a stark difference with when I had to try and get repairs done on a PC about a decade ago; maybe PC companies have upped their standards since then, but Apple still tends to be on top in the ratings and if my experiences are anything to go by, there's a reason for that.
The lesson I take away from your experience isn't to avoid Macs or iMacs, but to try and buy directly from Apple if you can. The subpar part of your experience really sounds like it centered around dealing with the third-party dealer.
