Look, art is always subjective. But art also creates a common ground for people to empathize over. So while "everything is always subjective" might technically be true - in reality it really isn't.
Like, if I personally say "Batman v. Superman did a lot of shit with iconic characters" - that might be my personal opinion. But one shared by a LOT of people. One that even is objectively quantifiable when looking at what kind of box office returns WB expected vs. what they got, and what the overwhelming common critical and audience reaction was. Sure - many people did like it. But there is also an objective component as how it simply was disappointing for many, many, many people.
The same holds true to a degree for DIS. Yes - it's entirely subjective, and people have every right to like, nah, unconditionally love the show. I like it a lot. But there is also the very objective statement that this show disappointed on a LOT of expectations, so much so that the creators felt the need to address these issues head-on in a completely on-the-nose way.
Well time is a good indicator of whether or not something is objectively art. People still love Shakespeare and think it's true art, and it's been around for hundreds of years. Yes, art is subjective to some extent, but you still do find a consensus at some point. In the end, though, it's still just entertainment so it's not like our feelings about it are a life or death matter.