whatever you think is fine. all I know is I tested my kitchen faucet with 50' long pc of 1/4" air hose & there was zero issues. there was zero difference in time when filling a given size container with either the 1/4" hose or the 40 plus feet of 1/2" copper . what was noticeable different was the length of time to get full hot water at the faucet. If & whgen I get around to repiping the faucet, I will have 25 to 30 feet of 3/8 soft copper. I call that a win .
3/8 OD is very common size in plumbing , it's not at all a difficult to obtain size. .
believe the textbooks all you want, I'll believe my tested facts too.
you have valid point if you're on a pump and have low pressure , but that's not my case
cheers !