... I would not call [capacity for hard work] the "only" quality. Rather, it is the most vital.
Magnus Carlsen, for example, clearly has some intellectual gifts that he developed into chess skill. But, without the intense work that he puts in, you would not know his name. He claims to have spent time studying 10,000 games. This study gives him an enormous array of tools for finding the strongest moves in the new positions that he encounters at work.
Without some capacity for memory, going through 10,000 games might have been a futile exercise.
What does it mean to say that a quality is “the most vital”? Is the engine more vital to a car than the gas tank?
Yes.
Cars run on several sorts of fuel. None run without an engine. ...
I did not ask about the sort of fuel. I asked about the gas tank.
There is no gas tank on a Tesla. The nature of fuel determines the method for storing it.
I have over 800 games and less than 800 rating. Maybe I should just stop playing and do like Tarrasch told, just study instead of practicing.
Yes. Increase your ratio of study to play, and that should help considerably.