I think the eivdence is substantial and written right through history of the specific aims of numerous of these wealthy families and their agents - including the raping of Africa and much more besides. In any case, setting aside the structure of it all - the financial changes you suggest are flawed in that the entire financial system and the property system attached to it is just as corrupt - meaning that there are hundreds of ways around any inspections of finances and on top of that, the power magnates already have all the money they can need or ever use - so unless there is a total reset I don't see any such limits being as effective as needed.

There is also the huge issue of blackmail of politicians (which is the norm now).

Beyond all of this though, the core issue remains, which is that democracy is fundmantally unfair and unbalanced since it is a group of people getting together to decide who should tell them what to do and more than that to specifically tell a percentage of people who don't agree too.. This is a huge issue and not one that can be fixed by control since it is a form of control in itself. Only the absence of control can solve such issues.