EXCELLENT in grammar has no comparative or superlative form, so we cannot say *VERY EXCELLENT.
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According to this rule, neither can we say SO EXCELLENT (eg * it’s so excellent!); do you agree?
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I’ve got a sentence:
-Your performance was so excellent that I’ve set you as my role model.
I think this sentence is grammatical and acceptable, because EXCELLENT is not modified by SO, and SO is used with THAT to introduce a that-clause, which is the result of the previous statement. Do you agree?