Pompeo has been given the role of a diplomat but he isn’t a diplomat. Trump is a diplomat. A great diplomat and a ‘people person’ like he likes to say. That’s why Trump gets results and goodwill where others dont.
Pompeo’s qualifications for his current role is that he is a Trump loyalist and shares the same worldview as Trump - which are very important qualifications but those don’t make him a diplomat. This is not a knock on Pompeo. Trump has an innate talent to persuade and influence people. If Pompeo were president or anyone else for that matter, there would have been exactly zero chance of the US/NK summit happening or any goodwill coming out of it.
On a slightly different topic I think Trump is right that China is now trying to sabotage this.