Netlfix's The Witcher is a typical "hang up the star and let's save on the rest" production, once you've secured one / two A list actors there's no way you're gonna hire more A listers unless you want to start to cut costs / recast if more seasons happen. If the show fails there's no question but if the show gets more seasons you'd want to be sure to retain most actors and don't want them doing other major gigs and fucking up your production schedule.
We're talking about Netflix, they now have a TV shows development department, they won't spend $200m on a polish written fantasy project which happened to become successful video games. They're preparing themselves for both Disney and Warner streaming services, It's not Amazon and their "find it yourselves" TV show policy, they want visibility and they'll make sure they'll get it with the money they intend it to.