If Hunter Biden wasn't worth that to those companies, then they didn't have to pay him that. Free market! As for Trump's children... would their own dad have fired them provided they were minimally competent enough to tie their shoes? Doubtful.
https://www.celebritynetworth.com/richest-businessmen/lawyers/hunter-biden-net-worth/
According to this, Hunter Biden is a 50-year-old worth $3 million dollars. There are doctors, lawyers, and other businessmen you've never heard of who have built up nest eggs by that age worth way more than that. In the context of international business... yes, that is chump change. If he's a grifter, he's not very good at it.
In comparison: I've seen estimates for the assets of Trump's children ranging anywhere from $25 million to $750 million. They're not that smart, honestly. Can you sit here with a straight face and tell me they all really earned every penny of that? Really? https://www.forbes.com/sites/chasewithorn/2019/11/08/heres-how-much-don-jr-eric-and-ivanka-trump-are-worth/#3e86d8c575ed