If you don't like them, you don't like them. Not everyone does, but a lot of people do (as you've clearly seen in this thread). At the very least, I feel like you've just had horrible luck with the lifespan of your Sennheisers. My bro has an HD650 and I have an HD600, both of which have been working for over a decade of pretty regular use. I've been quite careful with mine (same treatment as any headphones, tank or not) so I haven't ever dropped them.
Your dissenting opinions of the HD600 are fine as far as I'm concerned; everyone hears differently. One of my critiques of your thoughts would be maybe the bit about thin wiring. You should understand that in ANY electronics work of this type, wiring is often far thinner than you imagine it would be; wiring in headphones and earphones is vastly different than larger audio products such as speakers and can vary just on application within the same product. And really just in general, anything you don't see is going to use thinner wiring because it's exposed to less potential harm and didn't need to be as robust. It's how any company has to find the places where they can still make money on a product; a business is still a business. My other real critique is your thoughts about the driver's size and ability; really sounded like you've thought less of the headphone because of the driver size. Can larger drivers do better? Certainly. And the vice versa is also true. But even barring that, consider this: your Yamaha has a 40mm driver, your Roland has a 45mm driver. The HD600 uses a 42mm driver. While sound reproduction/fidelity can be subjective, it's objectively wrong to criticize the HD600 for the size of its driver as it's quite literally the average size of a dynamic headphone driver.
The other unlucky thing you've got going for you is that since you're purchasing in euros, it's a bit more expensive as the HD600 technically hovers around the $300 USD mark on average. Also, I actually personally wouldn't have said to get an HD600 anymore these days and the reason is simple: Sennheiser paired up with Drop (formerly MassDrop) to put out a "special edition headphone". I don't know about European availability, but in the US, the HD58X is available for $170 and to my ears, offers up 85%+ of the what I get from the HD600. It has a slightly different sound signature tuning, but it's not all that different from the HD600. Value-wise, it's obvious: 85% of the performance for 60% of the cost. And I had a pair of those too. I ended up gifting those to one of my friends because his AKGs died. But if my HD600s died today, what would I get? The HD58X because the price is right and the performance is far more than acceptable to my ears.