Or are you pretty sure that "suffering" is not just hard to define, but actually impossible, and/or that it's impossible to reduce suffering to any significant extent below the default outcome, while keeping technology at the same level?

Masochist: Please hurt me!

Sadist: No.

If you are pretty sure about this, are you equally sure about every other value that I could cite instead of suffering?

Not sure, but it might be impossible.

What if I said that I don't know how to define it now, but I think if you made me a bit (or a lot) smarter...

If you were to uplift a chimpanzee onto the human level and told it to figure out how to reduce suffering for chimpanzees, it would probably come up with ideas like democracy, health insurance and supermarkets. Problem is that chimpanzees wouldn't appreciate those ideas...