Whether original sin exists or not, nothing changes, does it? If there wasn’t original sin, then the whole Immaculate Conception wouldn’t matter, would it? It’s all relative to what one believes.
If original sin doesn’t exist exist, then sin is still absent and all things are good and there is no evil. Wait, that isn’t the case is it?
So sin is here, and renders us hell bound without redemption. So, yes the IC and Jesus DO matter. There is no relativism to it.