I think the point of Caicedo is not just to be back up to Casemiro, but also do the #8 role you mention to. And before you say he can’t, he plays the role already for one of the most progressive teams in the country / Europe with weaker players around him.
Personally I think he’d be our best option assuming De Jong is a non-starter. Very different player to De Jong, but there aren’t many players of De Jong’s style and quality, so IMO Caicedo would add as much value to the team, just in a slightly different capacity. The difference with signing De Jong is we would definitely need to still sign DM cover for Casemiro, whereas Caicedo could allow us to be our sole MF signing.
The other option for me would be Ugarte at Sporting who’s a similar profile to Caicedo and would be a fair bit cheaper, and then sign another more advanced 8 as well with the money saved.