How much of that is nostalgia for you?
I do think that a lot of the stories are better in the older movies and that many current movies are simply rehashes of older movies.
But it takes me a long time to get into the older movies, even the "really good" ones are robotically acted with bad camerawork. I don't necessarily think people now are better actors, but it's a style thing. In current movies people are much more likely to assume the role and make it look/feel natural. In the older movies they are clearly acting and delivering affected one-liners over and over; it's not a natural voice or delivery. It's almost like they haven't quite figured out the transition from radio just yet.
It's a matter of taste, of course.
Having said that, you're simply wrong
Seriously, I know what you mean, and it's true of a lot of actors. Generally, I think they were transitioning from the stage rather than radio. Some movies are essentially stage plays with a camera or two set up to photograph the actors.
And some actors aren't nearly as good as they're cracked up to be. Gary Cooper is a shining example. He was a personality and a movie star, not an actor. I'd put Clark Gable in the same general category. And yes, Bogart in a lot of his movies.
That's one reason "Citizen Kane" was such a revelation. It was made by a twenty-something radio guy who didn't know enough not to follow the rules.
But your brush is too broad. A lot of the classic movies are classics because they were just damned good movies. The one that comes immediately to mind for me is "Treasure of the Sierra Madre," in which Walter Huston gives what has been called the best performance ever by an American actor. (Of course, it was his son, the director of the movie, who called him that, but he had a point).
Now if you want to see REALLY BAD movies, sit down for a marathon of '70s flicks. They are, as a group, horrible in all respects, and terribly self-conscious in the process.