Pike looked young in The Cage. Anson Mount would be a better fit for Jeffrey Hunter Pike.
Oh yes, the resemblance is uncanny!
Personally I'd prefer if the TOS main characters were no recast. I didn't like the Kelvinverse recast and I don't want to see recasting in Discovery, whether it was those same actors or different ones. It is big universe, we don't need to see Kirk or Spock, or if we do, a few second cameo using old footage and CGI wizardry will suffice.
Though if they want to use CGI to create TOS character, the Discovery style hologram communication offers an interesting opportunity. As the holograms are translucent and a bit glowy, it can be used to conceal small imperfections in the recreations. Though I find recreating dead actors a tad macabre. If they want to CGI recreate TOS characters, I'd prefer if they'd stick to those whose actors are still alive, perhaps with the original actor providing the voice acting.
I'm not so touchy about characters that we saw only in few episodes, so recasting Pike is fine (and Anson Mount would indeed be perfect) and I liked Frain's Sarek well enough. Though there it seems unnecessary for the character to be Sarek specifically, it might have been better had they just created a new Vulcan character for Frain. And speaking of Vulcans, I'd love to see Jolene Blalock back as T'Pol, as dodgy as ENT was, she did good a job.