Saying that "but for" corporate/capitalistic influence, government would be benevolent is very much implying that countries without capitalism shouldn't have corruption.
I think the argument is that absent corporate lobbying, politicians can still be influenced. Something else will fill the position, and the total amount of influence over politicians not granted democratically will be unchanged. Maybe that's still through money, but taken as direct bribes under the table, or maybe it's populism, or something else entirely.
I don't know if that's true. I also don't know if what replaced campaign contributions would be better or worse.
I do know that lobbying is itself overstated. In 1999, the GDP was 10 trillion. 3 billion, or 0.03%, of that went into politics, mostly from individual donors rather than companies [1]. If lobbying were an effective way to buy political influence, more companies would shell out. Maybe it's already happening under the table, though.
There's a bunch of comments saying lobbying makes things worse than not having lobbying.
I don't see the ones saying that's the only source of problems?