I think something related to this was discussed on Geek Warning a couple of years ago in a discussion about the ring of death. I think it was specifically about how how the bearing seats in CF frames could “warp” as the frame cured, resulting in head sets that wouldn’t stay tight. I could have part of that wrong.
On the Cervelo end, I used to lust after a Cervelo Super Prodigy that was hanging in an LBS (photo is just a representative example).
My favourite topic! I’m with you on disliking headset routed cables. So much so that my two recent bike purchases have been explicitly chosen to allow external routing. I even persuaded my wife to get a crux based on the external cables too. Only a small crusade but doing what I can to vote with my wallet.
New gravel bike is a Pivot Vault which has options for internal or external (frame routed) cables. Only downside is that the fork cable is zip tied down the back - very old school.
You said not looking at custom frames but my custom Ti frame from Waltly (China) cost ~£1000. I did give into peer pressure to spec a headset that allows headset routing if I eventually get a wireless groupset, but it will only ever be the rear brake cable that goes through there.
