You will have to differentiate between you as an artist and you as someone serving your clients' needs.
You have full freedom to use any art form, in any way, to express your thoughts, emotions, impulses, and communicate whatever you would like to communicate. Anyone labelling that "wrong" deserve a punch in the nose, as there is nothing more fragile than an artist, not having any objective way to measure his performance, and a few guys out of a hundred have some joy criticizing the poor guy. The worst are who pretend to be nice and helpful: "You know, everyone talks about that you do not really grasp art, your knowledge is not sufficient. I am just trying to be your friend, and save you from embarrassment and wasting your money and time". You see and hear this guy, you instantly do a head kick, and I am not joking. Those are the one that, pretending to be nice, suck creativity out from artists. Critics, "everyone says that", "people rumour", now you know the recipe for handling.
Now, if your target audience prefers landscape, that is their preference. Everyone has the right to decide what is art for them, what is beautiful for them. This is influenced by culture, background, language, etc. No problem with that. If they want landscape, and they pay your bill, provide what they like: landscape format!
But never, NEVER ever believe that your art is in any way wrong. If a customer says that you do too much portrait, make a mental note that he wants more landscape. No biggie. If a customer says that you are WRONG by making too much portraits, make a mental note, that this guy is a jerk (or more preferably: the guy has not yet reached a level in human evolution to enjoy your art), but tell him that you will seek ways to produce art that is enjoyable for him. But that is serving your client and has nothing to do with how you perceive art.
But your art is your art, and if you like portraits, do portraits. If you want, do only portraits. If you want, create only circle-shaped photos.
The lesson I learned in my life is that if people criticize your art, you just have not promoted your art enough to find your right audience, who will be ecstatic about your art.