Right, so based on your correction that the SM is payable until he is 65, not her, what she actually was awarded was 57% of the marital assets, excluding his ring fenced inheritance and due to inflation, the 7% that comes from SM is actually worth less.
So again, it comes down to the detail and how you interpret it.
Would I pissed off at finding £2500 a month for a woman who doesn't work and is sitting it a big old house she could sell? Well, yes I would.
Would I think a 57% settlement excluding inheritance after a marriage of 18+ years where the wife was a SAHP and had spent at least 5 years abroad to support the husband unfair? No I wouldn't.
If you both don't like the monthly payments, why not use the inheritance to buy her out of that with a lump sum?
The total settlement of 57% really isn't unfair.
I'm a working (single) mother. I think kids are just fine with two working parents, if the childcare cover is managed well with good people.
But honestly... Why wouldn't many people want a SAHP?
I may get flamed for this - but you know what? I think a SAHP is better.
If I was wealthy and my partner had a low paying job that we didn't need the money from (you say she was a PA) then - as long as they were happy - I would rather have my partner at home. Right up to teen years. You often see people on here comment that they need you more as teens.
There was a value to her being a SAHP, and that is why she was awarded 57%.
I do understand that in a specific example, someone might be a lazy cow who spends the money on heroin instead of the kids 
But... Divorce settlements are not value judgements. And I really don't think you can argue that 57% is excessive.
I return to my original post... I think it's far more a concern that you are upset and not sleeping and moving home and changing your job... all for your husband!
All of this (IMO fair) settlement was in place 2 years ago. Before you got together. It is your husband who is causing the current situation - not his ex wife.