The problem with this picture is that the parliamentary fees office isn't the MPs' superior, it is their subordinate. You cannot pass the buck to a subordinate. This is not a case of your boss saying "you can claim for this". It is more like your secretary saying "oh yes I'd claim for that if I were you".
If the rules failed to specify appropriate limits for such things as cleaning then it is quite right for Legg to invent them. The rules are also MPs' property, and their flaws cannot be blamed on anyone else.
This is not to say that Legg has got it right. He seems to have ignored the real money-spinner of subsidsed mortgages. I'd rather my taxes pay for cleaning and gardening than for mortgages which fund capital gains that go straight into an MP's pocket. (Although having said that, surely you generate no more dirt by living in two places, so cleaning costs in one should be largely offset by savings in the other.)
Is it unfair? Perhaps if you are one of the noble few who tried to reform this system sooner. But if you're that noble, you can live with it. You can welcome the slow approach of sanity.