I think the LTB advice often comes from people who have done exactly that and realised how much happier their life was afterwards.
I LTB after advice on here that made me realised this isn't just "how men are" and that actually some men are lovely! I have found one of the lovely ones and if have a moan on here about him and someone tells me to LTB I won't because I value him and our relationship too much. I'm not an idiot, I just needed it pointed out to me that I didn't have an obligation to stay with XH if I was unhappy.
If I come across someone on MN in a similar marriage to the one I had with my ex, bending over backwards to try and make him happy when he won't or can't do the same, too right I'll advise they leave.
LTB and all the accompanying 'get thee to a solicitor, get copies of paperwork, get your ducks in a row' shizzle is MN gold. It's the equivalent of He's Just Not That Into You. Such a simple concept but so very often overlooked as the solution.
It's not always easy, it definitely has it's down sides (only this weekend my DCs were complaining about having to uproot their lives and go to stay at their dad's and I said "I know it would be easier if we all still lived here together, but we don't, so we need to make the best of it") but we all know that the rest of the time is so much happier and calmer.
As for get a cleaner or a nanny - a lot of people don't think realise that a nanny is an option when they're looking into childcare options - it seems extravagant but actually when you have 3 DCs it makes sense.
Similarly, get a cleaner and get your useless OH to pay if he won't do his share. Many women wouldn't dream of doing this as it seems like it's 'their job' and OH has to help out. Once it's pointed out that anyone CAN do it and that if OH won't then it shouldn't automatically fall to OP, it's quite liberating!
Going NC seems like a big step, but I've tried cutting out negative people from my life and while it is initially uncomfortable, it is also very liberating. I feel like a great weight has been lifted when I no longer dread what that text is going to say.