Well, yes, but.. It is not that the financial sector does not have its own rhythm, determinants and events. I think marx says somewhere that each crisis has to be explained in its own terms, implying that no grand theory can substitute for an actual investigation of events. Certainly he envisaged a lot of lassitude in the financial sector, in understanding that fictitious capital was at many removes from the productive economy. And certainly he seems to have thought it possible that it could create its own difficulties (as in the discussion of the Banking Act as an artificial barrier).
But you don't need to be Marx to see that the financial sector can only survive if it can coexist with social reproduction. If you cannot eat, you cannot trade stock.
As to models, no, I think you are wrong. Marx calls the 'departments' in volume two a schema, not a model. (i.e. it is a rehearsal of the outer limits of the system, considering its variables). And he thinks of the occ and the frop as logical reconstructions derived from abstract laws of capitalist production. They are not models.
Of course, he might have been talking out of his backside, but that's what he thought, I think.