Ferrari have pretty spent double what Merc have, they SHOULD have done better(and as of today are), so what. a team spending 180mil shouldn't beat a team spending 420mil, just shouldn't. merc have only upped their spending in the past 18 months or so.... even then it was to basically 200mil less than Ferrari last year and 75mil less(because Ferrari dropped massively, supposedly anyway) this season.
Rosberg has been crap this season and I really can't see how in what, 7 finishes Schumi has beaten Rosberg 6 times, while I'm completely guessing here, being outqualified in probably 5 or 6 of those races? Schumacher, race driving, has pawned Rosberg this year, if the car hadn't screwed up 4-5 times he'd be smashing Rosberg(he still might, Rosberg could have all his bad luck in the next races while Schumi gets points finishes in all those remaining.
I still don't think Schumi is back to his best, no reason he should or needs to be, the car isn't the best on the grid, they are competing almost exactly where you would expect given their spending. Lotus are having a particularly good year and Merc a bad on in terms of luck, finishes and car speed vs money next year could be the reverse, that happens. Lotus also have one of the best drivers on the grid, current form, Merc don't come close. Ferrari don't have the best car every year yet outspend everyone, its gives them a much better chance of doing better but there are no certainties.
The money spending will be vastly closer, it is closer this year already, the next few years the money gap will shrink and the number of years the teams have spent closer to each other increases.