My divine weapon does work I was just bring an idiot thinking it would one hit kill like my Helberd. When i faced Nito I tried not to go anywhere near the giant skeletons, just killed the smaller ones. Then put on my Power Within and attacked him when he lodged his sword in the ground.
I think you're ready for Gwyn. But I also think you said you wanna do other things. You can work your way up to the boss fog and go back out to farm titanite chunks. You get a bunch going to get Gwyn. I think you face 5 or six Knights and each of them always drops a chunk of something.
You get to him via frampt. You go back down under, feed the souls and a fog gate appears. go through that gate to work yourself to Gwyn... the second fog gate is where he'll be. So if you don't want to face him yet just turn back around or homeward bone out.
Great place to farm chunks though. I think I died to Gwyn no less than 20 times so on my first playthrough I had a ton of chunks ready for new game plus
I just need to kill Seath and the Four Kings then I'll probably give Gwyn a go. At the moment I'm mainly just farming for chunks/shards, but the places you mentioned seem like the best bets to get them. Only doing Blighttown and the slugs at the moment. I'm just building some weapons with the Embers that I have collected.