So if the opposition only has 5% support, while the establishment has close to 95% support (for the sake of the example).

I'd argue the opposing party 5% support would likely have a matching resource pool of their size. Meaning the establishment might run 95% of all ads as ads supporting the establishment and only 5% of ads would support the opposing party. So I struggle to see how that would help the opposing party?

Obviously, it isn't that cut and dry, but America is a good example actually. Because they have 2 major parties and several third parties. But those third parties never make any meaningful growth even after running ads because they only represent >5% of the available political parties.