I had a co-worker last millenium with a higher end, Miyata sport bike that he broke repeatedly at the brake cable exit just forward of the seattube. He was 200 pounds and rode it every workday for a 40 mile round trip. (Viet Nam vet with PTSD, issues and no license.) Miyata kept giving him new frames but seemed slow on the learning curve. (This may have been a case of exiting the cable forward of the tubing butt.)

If you run continuous housing, the effect on rear brake performance is the same as running that housing through TT braze-ons like was done for so many thousands of 1980s bikes. Well except the internal route requires sharper bends at entrance and exit. The TT full housing run is my preferred because it moderates the effectiveness of the rear brake relative to the front. (Less power back there, more control in hard stops. Fewer crashes.) Running bare cable completely unseen with bends at each end always seemed to me a very bad idea, especially for a brake. I'll run continuous housing secured with clamps on bikes with stops for bare brake cable runs.