I agree with you. You have a valid argument.
But I have to ask myself why does the law include the word heliport? They had already used the word airport earlier in the sentence. So isn't heliport redundant? It appears to be.
Or is it? After all, in sec 336, they didn't bother to use the word heliport? Why not? Is it possible they purposely included it in Sec 335 and purposely excluded it in Sec 336?
AC 91-57A is almost a cut and paste of Sec 336. That was another opportunity to take the mystery out of the equation by including "heliport" in that document, but for reasons unknown, Ms. Ray decided to leave it out. Why? Might be because she didn't want to differ from how it was written in the public law.
Bottom line for me is, the word was included in Sec 335, and excluded from section 336, and that makes the situation re heliports ambiguous. Others will not agree with me, and that's fine.