Some correction:
This is completely the case in US, but not the case in EU (I look to my country as example, but systems in EU countries are often very similar (because countries compete in various ratings and so copy good ideas from each other)).
Political parties are financed with all kinds of other mechanisms (3-4 different transparent sources, and corporate funding maybe is completely illegal or tiny). But general lobbying is legal, so politicians still work for special interests who have most access to them.