For now my "endgame" is the Hifiman HE400se. I can describe it similarly to how you described your Sundara. Super clear, great extension on both ends, nice fitment, but a little on the heavy side.

These cans impress me a lot, especially now that I have a $600 speaker setup for my desk and these headphones sound a lot better in terms of overall detail and extension but not when it comes to staging scale or pure enjoyment.

At the moment it is difficult for me to feel a need to upgrade my headphone setup as the quality of the HE400se already feels amazing, the value is truly great. So when I eventually upgrade, it will be a big one and not a side grade.