I haven't listened to a DT770, but your ears don't lie.

However, the problem is two fold.

One, you comprehend only upon the sum of your experiences. This goes for both of you by the way. You won't appreciate the capability of something or understand its shortcomings without experiencing the greater breadth.

Two, human hearing is NOT static. Our minds constantly adjust to balance out common sounds. Your mind will "tune" to what you experience a lot, and that sound will become normalized. It can take work and training to actually detuned and be more unbiased. You will also need equipment too. For example when I get new equipment, test, and review I use an array of other headphones as static, known points along a measuring stick. I also use test tones and pink noise tracks to aid with EQing and seeing how the product produces sound and forms the notes. And the process to fully learn and understand a single product well takes weeks of daily listening, testing, and comparing. All of this is done to tune out the bias and accumulate details.

Companies like Logitech make good headphones. They make products that hit center mass in the market space. They are all around good but at the same time not amazing either. They just don't do anything terribly wrong. And for this market space, that performs and sells well. It's also why companies like Steel Series is very popular because they do the same thing.