That kind of depends on your definition of "easier"...I mean, you still have to eventually go through it at one point...If you do it later you'll be at higher levels so wouldn't it be "easier" that way? Most battles down there can be avoided though so I don't see a problem either way. It's nice sometimes to do it later because there's one little dialog trigger before you go down a level in the sewers that normally you'd only get to see Marle & Lucca's, but if you save it for later you can have a different party (though it's not a great big hunk of dialog...I think everyone basically says that it's creepy or something)...
And, yeah, I didn't know people didn't know he was alive at that point...I mean, people in the domes kind of talk about the crazy guy living at the other end of the sewers or whatever...