Microwaving isn't inherently bad. But there are a lot of ways it's easy to misuse a microwave, and a lot of things a microwave can't do. It's telling that the example that you gave involves using the microwave in combination with other cooking methods.
If you're using the microwave to fully cook the food, it's inevitably going to be like you unevenly boiled/steamed it. If all you're doing is heating up a fairly liquid soup, that's fine. But it'll also tend to make mushy vegetables, unevenly cooked meat, and so on. And it can never really brown things like you can easily do on a stove or in the oven. In that sense, it really is bad for the structure of the food.
Your example of briefly microwaving chicken before roasting or grilling it? Sure, that saves time overall, and it works out well. But it'd be easy to mess up if you're not familiar with the microwave and end up with chicken that's overcooked in spots, and it takes more active work time than just popping it in an oven and forgetting about it for a while. If you really want good results and to save time, then instead of using the microwave, you'd cook the chicken sous vide, holding it exactly at the "done" temperature, and then pop some out to roast/grill to finish as needed. That's faster, less work, and more reliable.
So, sure, microwaves can be very useful, and if you know how to use them well, they won't mess up your food. But most people use them in less ideal ways, and it makes sense to discourage that kind of thing if you want good food. It's possible that some cooking shows exaggerate or overgeneralize this, but the core is definitely true: trying to do too much on a microwave can make awful food.
And the tradeoffs you're willing to make in your home kitchen aren't the same ones you'd want to make in a professional kitchen. If you can cook a dish faster, but it requires your attention for more of the time, that's worth it at home when you're just making a couple things. But if everyone's busy all the time cooking at a larger scale, you care about the amount of work time it takes, not just the wall clock time from start to finish. There are easier ways to save time, especially in a restaurant kitchen.