T1.1 is a very well balanced headphone. It was known as the jack of all trades when it came out compared to the HD800. The reason a lot of people have issues with treble with the T1 is because they don’t realize that the headphones jumps up to 1k Ohm impedance at lower frequencies. With modern amps, the OI is lower to accommodate for more headphones and to have a higher damping factor. Generally this means that a lot of amps aren’t able to provide the voltage that high impedance beyers need to produce a more balanced tonality which leaves the treble to be more emphasized than the rest of the range. Also, cheaper dac/amps have more glare than the higher end offerings which will make the situation even worse.
Long story short, T1 is a good headphone but does require the correct dac/amp (OTL tube amp) to go with it. The way amp manufacturers have been designing their amps means beyers get a really bad rep with high impedance drivers. That’s one of the reasons all the new beyers have lower impedance drivers now.