Alternation between が and は in seemingly identical sentence structure


I found the following sentence online; it's a comment about three players A,
B, and C that regularly compete against each other.

> Aに勝てるのがBだけでBに勝てるのはCだけなの良いな

To me it seems like the structure of both subclauses (Aに勝てるのがBだけで and
Bに勝てるのはCだけなの) is really similar, so what warrants the change from が to は in
this scenario? Is it the proximity of the latter subclause to the main
predicate?




This is a case where multiple means of emphasis, namely the cleft sentence
structure and だけ, and multiple possibly contrasting statements are making the
choice of the right particles hard, or in a way easy as all combinations seem
fine.

> Aに勝てるの **が** Bだけで、Bに勝てるの **は** Cだけだ。
>
> Aに勝てるの **が** Bだけで、Bに勝てるの **が** Cだけだ。
>
> Aに勝てるの **は** Bだけで、Bに勝てるの **は** Cだけだ。
>
> Aに勝てるの **は** Bだけで、Bに勝てるの **が** Cだけだ。

The first pattern, with が and は in that order as in the original sentence,
sounds to me like it is explaining the rules centering around B. It first
states a characteristic only B possesses, and then goes on to explain another
characteristic of B in terms of its power balance with other things.

The second and third sentences seem to give equal weight to B and C (which
come after が in the second), and A and B (which come before は in the third),
respectively.

Only the last one sounds slightly off to me. The first part seems to focus on
A, but it is not even mentioned in the second part. If anything, the sentence
sounds like an explanation about what C is like, with additional information
about what it is not: It is not the one that beats A because that’s B.

Without だけ, the first combination sounds a bit weird to me, at least unless
someone has asked what B is like to solicit this statement. Otherwise, the
exclusive focus on B in the first part of the sentence seems unwarranted.

> Aに勝てるのがBで、Bに勝てるのはCだ。




This is a case where multiple means of emphasis, namely the cleft sentence
structure and だけ, and multiple possibly contrasting statements are making the
choice of the right particles hard, or in a way easy as all combinations seem
fine.

> Aに勝てるの **が** Bだけで、Bに勝てるの **は** Cだけだ。
>
> Aに勝てるの **が** Bだけで、Bに勝てるの **が** Cだけだ。
>
> Aに勝てるの **は** Bだけで、Bに勝てるの **は** Cだけだ。
>
> Aに勝てるの **は** Bだけで、Bに勝てるの **が** Cだけだ。

The first pattern, with が and は in that order as in the original sentence,
sounds to me like it is explaining the rules centering around B. It first
states a characteristic only B possesses, and then goes on to explain another
characteristic of B in terms of its power balance with other things.

The second and third sentences seem to give equal weight to B and C (which
come after が in the second), and A and B (which come before は in the third),
respectively.

Only the last one sounds slightly off to me. The first part seems to focus on
A, but it is not even mentioned in the second part. If anything, the sentence
sounds like an explanation about what C is like, with additional information
about what it is not: It is not the one that beats A because that’s B.

Without だけ, the first combination sounds a bit weird to me, at least unless
someone has asked what B is like to solicit this statement. Otherwise, the
exclusive focus on B in the first part of the sentence seems unwarranted.

> Aに勝てるのがBで、Bに勝てるのはCだ。

