It's a tricky problem. Banning political spending for for-profit organizations is an easy win, but not a particularly big one. The big issue is PACs, and I can't come up with clean line to draw between "me and my friends got together to oppose evil policy XYZ" (which is clear, unambiguous 1st amendment activity) and "me and my billionaire cronies got together to oppose good policy ABC".
I would love to know what % of PACs - weighted by size (or “voice”, as you call it) - are operated as truly grassroots organizations with a normal distribution of contribution size. I’d put my money on <5%.
My solution is pretty simple. Do away with political donations altogether. People can still get together and make signs and go door to door for a candidate. And split the cost of pizza among themselves.
And that's basically impossible to curtail, without seriously violating fundamental 1st amendment protections.