In the first episode, Uncle Boris kept telling JN about how "British" he was when he (JN) was giving Boris the poker face. But I don't think the wooden poker face is supposed to be British - I think it's meant to be a product of the years of bullying at boarding school.
(I think the two key things which were supposed to reveal why JN is the way he is were his interactions with Uncle Boris, who represents Russia/traditional gangsters/his roots, and with his awful smarmy "friend" who offered him such brutal terms to save his company - reminding JN that however hard he pretends to fit in in London, to most people he will never be anything but "Godman" the Yid.)
I think the character has been slightly over-manufactured, in that he is supposed to demonstrate to us the dreadful alliance of traditional gangster networks + Panama Papers-style City money laundering that comprises modern crime networks. I don't mind this, because I think it's a good way for a drama to tell that story, and I have a soft spot for the buttoned-up/childhood trauma aspect (and this is a reasonably new way to approach it - we've seen so many gangsters along the lines of Tony Soprano who are messed up because of terrible parents, I like the angle that he's messed up not because of his parents, who both love him very much and did the best they could for him, but because of the boarding school + culture shock).
But I can see why people just don't like watching it (we have seen it before tbf). And I can also see it stretching credulity a bit, as while real people like Alex Godman do exist, they are way more likely to be living the Made In Chelsea life like Katya is, than building elaborate transcontinental crime networks!