It's very common to see small groups of kids traveling on the subway alone to get to school and they are perfectly safe.
Cultural events in New York city span all 5 boroughs, by the way. Central Park and "downtown" are by no means the cultural heart of the city. Have you even lived in New York???
Of course the state of the subway is a reflection of the city as a whole rather than an isolated issue, and that's true everywhere in my experience.
I was mostly in LIC and Manhattan though. Maybe it's not so dirty in the other boroughs?
Then when the pandemic hit and NYC was devastated, they were practically holding group orgy parties to get each other off about the fall of the city.
Then when the city started bouncing back it became "Well no, it's bouncing back as a dangerous crime ridden hell hole."
The "NYC is dangerous" thing is literally just conservative cope for the failed collapse during the pandemic.
Yes, the mega events are at Lincoln Center, Broadway, the Met, but that's very much like saying cultural TV is only on ABC, NBC, CBS, and FOX.
This does vary depending on the train and the station (I might recommend a tourist to avoid some stations on the J train at 3 am), but overwhelmingly most of the subway is safe at night, and more comfortable than during the day since you can actually get a seat. I ride it late at night, and so do many people I know.
So you've never been to Port Authority...