"So hard that it's impossible."

So a friend of mine and I were having an argument over this phrase and if it's grammatically correct.

"Something can be so hard that it's impossible" lets say that's party 1.

Party 1 argued that because hard can be defined as a great amount of effort, and that impossible can be defined as such a great amount of effort that it's impossible, it's okay to use the phrasing "so hard it's impossible."

Party 2 agreed that hard could be defined as a great amount of effort but disagreed that hard still applies when the effort is so great it's impossible.

Party 2 argued that hard, impossible or easy etc is a categorization of level of difficulty and that they are all mutually exclusive, you cant say its so easy its hard the same way you cant say its so hard its impossible.

Party 1 agreed that you can't say it's so easy it's hard because their antonyms. They argued that if you were to lay out a scale with 1-4 being easy or normal difficulty, 5-10 being hard and 11+ being impossible that anything above 5 all the way to infinity is classified as hard (until you get past 10) and then so hard it's impossible.

We were going with the definition of "A great amount of effort" as the definition of hard.

Party 2 argued that something being hard indicates the possibility of achievement of something, albeit with great effort, meaning something being both hard and impossible or so hard it's impossible cannot be used because impossible excludes the possibility of achievement.

We agreed that our argument was going in circles and that one or both of us probably lacked the correct methods or understanding of the mess of a language that English is and that's why I've come here, hoping one of you can dissect our logic and give a definitive answer.

Thanks for reading.

tl;dr

Is hard mutually exclusive with impossible.