Well, the most obvious differences between Conan and Jacob is that Conan was what his creator, Robert E Howard (who struggled his entire life with the pressures of society and toxic masculinity) not-secretly-at-all yearned to be and Jacob is the Stephanie Meyer’s idea of semi-exotic potential boyfriend. Check out this classic depiction of Conan by Frank Frazetta and try to remember the last time you saw a guy like this on the cover of a romance novel.
What makes guys sexy to women (physically)?
Well, it turns out since women are not a monolith and women don’t get to dictate beauty standards for men there’s no real standard.
Research has shown that men in general overestimate how much muscle women find attractive. They also tend to overestimate the importance and the preferred size of penises. (Seriously guys, don’t send unsolicited dick pics and don’t expect bragging about ridiculous endowment to help you)
Honestly though, the notion that you have to adhere to beauty standards in order to make a character attractive is kind of ridiculous. I mean, butts are sexualized across genders. Feeling comfortable pressed up against someone and kissing them is usually a plus. Looking like they may find you interesting as a person or want to impress you are definite help.
When designing a sexy male character: Leave the books about primary and secondary characteristics alone and forget about what manly men say a man should be like and ask, “What’s she going to like in this guy?”
Nothing is genuinely universally attractive, but at least this way you have a chance that the audience will see the appeal even it’s not for them.