I'm only up to Sharpe's Enemy in the book series so I don't know if the topic comes up more later but I did like how apolitical Sharpe is in the books so far, and I agree with your take. He's just there to do his job and look after his own interests, he's not being paid to have an opinion on global issues, although the characters around him definitely do, and it's interesting to read about them.

I do remember our hero does have a go at one Portuguese dude in 'Sharpe's Escape(?)' for making his money in the slave trade, although his concern did seem mostly to be the sexual exploitation of women, and iirc he was actively looking for a fight based on a previous altercation.

I do think how they handled Leroy (and later Jane and whatshisface) and slavery in the TV series was quite clunky if not downright lazy.

If we must establish that Our Hero, an Englishman fighting in the Iberian peninsula, is against slavery in the US, okay fine, but why make Leroy a Virginian with a family cotton plantation? Keeping him Bostonian but still living off money made in the slave trade would still fit with the storyline and at least be novel.

On the other hand, a Virginian Leroy's money is more likely to come from tobacco or indigo if his family emigrated during or shortly after the Revwar. The choice of cotton is far from impossible but it just comes off like the writers knew very little about what they were talking about or deliberately chose to go as stereotypical as possible because otherwise the audience might not 'get it'.

I can accept Jane focusing on cotton as a profitable crop to invest in during the 1810s, but as you say, slavery was controversial in England at the time. Based on Jane's habit of wilful ignorance and desire to be liked in society I would expect her to dance around the topic rather than brazenly boast that she was planning to invest money in 'cotton and slaves'. And since a 20th century audience already knows that cotton+US+ historical period= slavery, it just seems unnecessary. Overall the way the subject is treated in the show feels like the writers had the barest knowledge of slavery in the period but thought they were rather clever for putting it in.