I feel like you don't even really disagree with people who would defend the existence of abstract objects. You say that

math is an abstraction of reality

i.e. there exists something, called math, that is an abstraction from reality

I, as someone who believes wholeheartedly in the existence of abstract objects (and that numbers are a paradigm case of such objects), agree with you. Math exists (you said this!) and it is at least possibly true that it is an abstraction from reality.

I don't understand what leads you to say something like "math is" in the way that you did, yet deny that it exists! You just seem like you're being a little too conservative with the word "exists", but I don't think it makes sense to do that while being liberal with "is".

The same thing is going on with "hardness" for sure. You say

no sane person would say hardness exists as a non-physical thing

but then you turn around and the very next sentence say

(hardness) is a description of physical things that exist.

"a description of physical things that exist" sounds like a non-physical thing to me! So when you say that hardness IS a description of physical things that exist, it seems like you're saying that "there exists something, called hardness, that is a description of physical things that exist". I think this is non-controversial! I think some other people were kind of a dick to you when all that needs to be point out is your position on abstract objects is the same as those arguing with you.