So Sawa in another thread says that こと cannot be used in the example below. Even though it performs the same function as の (as far as I can see).
料理が(前より(もっと)) {上手だ/上手い/上手になった/上手くなった}
料理するのが(前より(もっと)) {上手だ/上手い/上手になった/上手くなった}
*料理することが(前より(もっと)) {上手だ/上手い/上手になった/上手くなった}
So what is the difference between the two that one can be used but not the other?
The difference is difficult and the linked question gives a decent explanation, but here is my two cents:
When you use 料理するのが, it immediately feels like there is a direct actor involved. If you look at all the examples sentences in the link, when you use の, it puts a focus on the fact that somebody is performing the action.
However, when you use 料理することが, the focus is no longer on the actor involved, but the action itself. If I would translate the third sentence into English, it sounds to me like the following:
The act of cooking has become better.
I realize that the above sentence is unnatural English, but my point is that the difference between の and こと is whether the focus is on the actor or the action itself.
However, my above explanation might not fit every pattern, so I would take this as general advice. For example,
サッカーを見ることが好きです。
In the above sentence I am using こと even though the act of "watching" has a direct actor involved. I believe the reason why こと sounds better here is because the act of liking is focused on the サッカーを見ること which is the focus of the sentence.
It's a very rough and shallow answer, but:
You can be good only at doing the tangible thing. It's meaningless to be good at an idea.
Just remember that with "上手だ", it's "の" that works for the reasons I mentioned. With other "verbs," more complex explanations may be required, and have partially already been discussed here.
