You obviously need 20 battens to support at least 5' of roach to get the sail area you need in the "Dead Sea", often called Chesapeake Bay.
Your sailmaker is correct. Full battens will provide maximum longevity in the sail. The difference in weight between the full-battened version he suggests and the long & short mix you lean towards may be as much as 10 to 12 pounds. Not really a big difference to hoist. The version you favor may be cheaper because there's less labor & materials. The longevity factor is difficult to gauge. Ful battens down low don't have as much work holding the sail flat as the upper ones tend to, so (as you sort of already determined) they're not as valuable as full upper battens. Try it half and half and see if you like it. Works for us.