Cinema has changed a lot over the past 100 years. Acting has evolved from the over acting of the early days to a much more natural, raw, style of acting. Just because Ryan Gosling has a different style to Errol Flynn doesn't mean that one is better than the other. Both eras have good and bad actors, and we should learn to appreciate both.
It is always hard to judge generations of actors, or any other type of profession for that reason. People ask similar questions when it comes to sports. I see no reason to think actors are any worse, or better for that matter, than they used to be when Peter Vaughan was acting.
Acting anymore is anything that anyone wants to record and put on YouTube. The things that are offered on Netflix are often not better than that anymore. The actors today have so many opportunities to act that even bad ones get parts. This isn't to say that it's good or bad, but acting is not as selective as it used to be.
Not saying that there are fantastic modern actors, just that many people act for money now. Money has always been an object but classic actors brought new material to the table that many actors simply base their routine on. They were more original and genuine as to where the industry now is very large and there are a lot of people with many variety with not much originality.