If you believe that 1b is a good rewrite of 1a, then 2b is an equally good rewrite of 2a. Whether the first judgment is true, however, is not obvious. There's nothing grammatically or semantically wrong with 1a or 2a, so why is there a need to rewrite them? The only reasons I can see are style and register. Context is what determines the need for style and register changes.
Both "a" sentences use a formal and, perhaps (depending on one's ear), stiff or even stilted type of language that may, nevertheless, be appropriate in its original context. Both rewrites, although perfectly grammatical and idiomatic English sentences, are slightly verbose and can be rewritten as:
1c: It is surprising that he is not the best player. (more formal)
1d: It's surprising that he's not the best player. (less formal)
2c: It is possible that he is not the best player. (more formal)
2d: It's possible that he's not the best player. (less formal)
"Good rewrites" is a subjective judgment. Making that judgment depends both on the criteria being used to judge the rewrite and on the person making the judgment. In other words, personal taste and the criteria for judgment must be considered before making a value judgment.
What criteria are you using to judge these sentences and rewrites? No one can argue with your judgment if they don't know what it's based on.