I can't think of any better wording to express the sense I want to convey.
To whatever extent, this thing seems unimportant to you, we need to rethink seriously about it.
The sentence wants to convey that someone X thinks something is not that important and another person Y doesn't agree with him, then the later says the former the aforementioned sentence. But to me the sentence looks a bit stilted. Is it natural way to say so?