I had brand new hammers installed some years ago (Abel, if I recall correctly) so I guess that should be ok. You're not suggesting they should be needled every year or so ? I fear that softening the heads would not only make it sound more mellow but also more dull, which would be bad as the sound is not the brightest to start with. Anyway I should not be blaming the instrument for my problems with bringing out dynamics
I don't know after how many working hours one needs a re-needling. And you never told so far how long you practises! So, normally I also would expect that some years it should be ok without that. But you surely got an initial needling after installation of new hammers!??
I may be wrong but I thought that needling turns a hammer from bright to mellow foremost. Dull is to me the opposit to long sustained. Maybe that has more something to do with soundboard, strings, how the sound is transferred?
Also, your piano sounds more bright than mellow to me, at least in your "default" keytouch.
At least the preconditions on the piano to bring out dynamics comfortably more easily one can meet, the rest is of course up to us.