Interesting. I need to get a new phone soon. Is the HTC 10 a good option? I have been on iOS for years with a company-provided phone but we are parting ways soon. For a personal phone audio quality is most important to me and I won't use many other functions.
In my opinion yes. I seriously doubt you will hear a big difference between your current portable setup and the HTC 10. I can't hear a big difference when I use my U12 or B&W P7, I actually prefer my U12 with the HTC 10. I would never use the HTC 10 with the Amiron or the DT 1990. But all this is of course just my opinion.
It really depends on who you ask... I found that even FiiO X5ii was much better than any phone I compared it with back then... Smartphones have their own limitations, depends what you'll be plugging into them - consider things like: There is a reason why X5-3 costs this much and is bought so well - the sound is really a thing of its own.
Can I ask which smartphones and headphones did you compare. There are several smartphones today with very good SQ. Cost is not necessarily a parameter that can be used. And just to be clear, I have the FiiO X5iii and like it very much .