People who call themselves "capitalists" typically want to reform the political end of things so it stops distorting the economic system.
This is not an example of No True Scotsman. Just an example of criticism that should be labelled differently.
The specific criticism offered, namely companies retaining power due to legislative or regulatory influence, is at its core a political problem (with political solutions -- changing the way regulations and regulator-business relationships are handled.)
"Economic and political systems are conceptually different, though there is a lot of feedback between them."
this reminds me of wave particle duality. energy/matter qua wave is conceptually distinct from energy/matter qua particle. but there is no question of "feedback between them". "they" are both just analytic vantages on the same singular phenomena.
If any thing regulatory measures are actually designed to prevent this. Whether they are effective or not is a different story.
Again, people who call themselves "capitalists" would generally like to reform the regulatory/legislative system so that it supports, rather than distorts, the market.
I just noted that the specific criticism given wasn't a criticism of capitalism itself, but of the government system of regulations and legislation that we have tied to capitalism.
It would be similar to, for example, criticizing the Soviet Union for corruption and calling it a critique of socialism, or criticizing a software company for stealing another company's code and acting like that was a critique of the extreme-programming process they were using. Valid criticism, sure, but not of the thing it's said to be of.
There are plenty of valid criticisms of capitalism, communism, socialism, extreme-programming processes, and so on. But there are also plenty of criticisms that are misattributed to one of those things, which IMO harms our ability to create solutions to the problems.