@Jean Szulc @Tónskáld
I share and understand your concern about this issue.
Many factors affect the answer (if there is one).
what is your (our) goal when composing?
how have you studied, how have you arrived to composition?
how restless are you about expanding your composition tools?
Perhaps, professional composers would try to define his/her own language? Which I assume, it is quite difficult nowadays. But notice that the vas majority of the great composers of our days have or had not focused only in one language. Richard Strauss, John Cage, ...... Gorécki, Párt, Vasks, etc., etc... Some of them experienced phases but also many others can be defined by a word: eclecticism.
I am amateur composer. I mean, I study music (a lot) and write music because I love it, it's almos a vital need. It's been a very long and satisfying journey to learn all the things I know. When you study new languages, new systems, it's normal you focus your composition on them. I understand this as exercises, but it doesn't mean you can do beautiful things.
But my final vision of this question is I have lots of TOOLS to use at my convenience, and when I want to. Starting on classic tonal harmony and counterpoint, but going to atonality, polytonality, impressionism, PC sets, polychords, Messiaen, mirrored harmonies, new forms, jazz harmony, and a long etc... I believe everything can be combined. The difficulty is to make something expressive with the tools you pick up for a composition.
So, eclecticism is the answer, for me.
I'm also convinced that a composer with aspiration to evolve has to study and know as many tools as possible. No matter you hate atonalism, you need to know what it is and how it works. We see atonalism mixed with tonal music in many great works (The Rosenkavalier, Cabaret, Psycho.....). If you don't know this tools, you are limited.
I respect people who write music imitating Mozart or Bach or whatever. What's the point? I understand to do it as exercises, to learn those styles. Nobody (of us) can make music 50% as good as theirs, in their strict style. They are happy with it, writing music like that. But I don't understand to be stuck in that period and nothing more, with all there is. Even if you hate atonal music, you can enrich your tonal music with many tools from the 20th century. So, it also depends on "how restless you are". I always value the hard work of composing in any style, but I think many people loose opportunities denying anything further than romanticism. I usually write music based in contemporary tools, but I don't mind mixing with tonal music if I need it.