But it has to be up to the author when they feel their work is ready for sending out. Novels are the writer's precious baby, and everyone would think twice before placing their baby on the floor and inviting kicks.
And yet we have to do it if we want to be published. We have to accept that our beloved babies will probably not be appreciated by everyone that claps eyes on them. Writers have to have both a sensitive soul and the hide of a rhinoceros. The truth is that not everyone will like everything, and the best thing for us to do when we come across some negative feedback is to scoop up our baby, dust it down and move swiftly on.
And actually, rejection isn't so bad. Oh yes, it hurts at the time, but it inspires you to do better, to try harder (that is, if you don't give it all up). It teaches you to investigate what isn't working and what is, and how you can make the former bits more like the latter. I now know the novel I first sent out was simply not good enough. Rejection made me pull it to pieces, and then rebuild.
Whichever route you take, either editing more and more or risking sending it out before the novel is ready, you have to prepare for rejection at some point. But you only lose if you stop writing. Keep at it, whichever your path. Push on!