You say that in this context, "extreme" and "gross" are not interchangeable.  That's incorrect.  I went to the trouble of researching, on a data base used by lawyers, cases that deal with both terms.  As I pointed out to you, at least one case expressly says "gross negligence means extreme negligence."  And I told you I could cite many more cases that equate the two.   You respond with a conclusory  statement that "extreme and gross are not interchangeable adverbs [sic]."  Not only the courts, but learned laymen, disagree with you.  The on-line Oxford English Dictionary says that "gross" means "very obvious and unacceptable."  The OED says "of conspicuous magnitude; palpable, striking."  Webster says "glaringly noticeable."  Extreme negligence, then, would be even WORSE, in laymen's understanding, than "gross" negligence.   What reasonable layman's adjective would describe negligence more extreme than "extreme" negligence?  Your contention is wrong and desperate.