Fast caramelized taste for soup

Without seeing the result and knowing your exact technique, my best guess is that you're not using enough liquid, or that you're using heat that's too high. High heat will essentially fry the onions, like you would expect by dropping chicken or potatoes into a pan full of hot oil.

Properly caramelized onions should take at least 20 to 30 minutes, I try to go for an hour whenever time permits. I actually stir as little as I can without allowing them to sit long enough to burn. Over-stirring shouldn't be a problem; under-stirring may be.

To start, you want the bottom of the pan to be covered with a thin layer of oil, and then make sure you stir the onions very well to coat them completely right after you toss them in. Begin with the pan on medium-high heat to get the oil up to temperature, once it ripples and you put the onions in you can lower it quite a bit. I rarely put it above 5 (out of 10, glass-top stove), and if I see things going crispy, I'll often drop it to 4. I'd rather take more time and have softer onions.

Are you adding any liquid along the way? Sometime, when doing large batches, 15 minutes in I find that I don't have enough oil in the pan, and I can see them starting to crisp up a bit more than I'd like. When that happens, lower the heat a notch, and add a touch more oil (or, as I prefer, a cube of homemade stock) to the pan. It'll take some practice, but eventually you'll be able to know how much liquid to use instinctively. The reason I prefer stock for my "second add" is because I know the stock will evaporate off, as mentioned in the question you linked to, you don't want to be pouring off flavor at the end of the cooking time, so evaporation is a good thing!

If you're using cast iron, I recommend trying stainless steel, I get much better results with the latter than the former. I'd guess that it's because I can dynamically regulate the temperature better with the stainless steel - with cast iron, once you realize you're at too high of a temperature, it's hard to lower it quickly.

If you need a step by step guide to start you off until you get a feel for everything, there is a great guide here and another here. The difference is that one recommends 1 teaspoon of oil per onion; the other uses 3 tablespoons per onion. I find that for my kitchen, it's somewhere in the middle (I just eyeball so I can't give you an exact number, unfortunately) - but if you try both methods on your stovetop you should be able to use that data to determine the right amount for you.

Walk away.

No, really - it works. Once you add the water to the sugar, it will likely harden and clump up (I don't know how to stop that happening). But once it does, you can just walk away, and leave it to sit till it cools down.

A lot of the sugar will just dissolve on its own, given time and enough water to dissolve into. Some mixing (occasional stirs as or after it cools) will dissolve some more. And at the last, when most of it has dissolved, you can gently start heating the pan up again, stir it around, maybe bring it to a boil for a bit, maybe add a bit more water and heat some more to get at those last undissolved chunks...

It's sugar, in water. It will dissolve until the water's saturated. It takes time to dissolve on its own, and that's annoying if you want to use it right away - hence measures like heating, or stirring, or crushing the dried caramel to stir into water that way. But it really works just as well, and is less tedious, just to give it some of that time and let it dissolve away.

I did this when making a caramelized burnt-sugar syrup, and it worked. Adding the water was pretty spluttery at first (the caramelization had to be stopped pretty fast), but I did notice the caramel hardening to the bottom of the pot once it had settled a bit. I gave it a few stirs, and walked away to take care of something else - and by the time I got back to it, most of the lumps were well on their way to dissolving.