Tanbark sails generally have a shorter lifespan than a good quality white Dacron. Tanbark is considered a novelty cloth and so is not made to the same standards as a higher performance sail cloth. Atkins drawings show roach so he at least intended for the boat to have battens. I don't know where Brent finds his stock of contrarians but the current offshore cruising standard mainsail has battens to increase the life of the sail,decrease heeling, and give better performance.
I met an Alaskan on Raiatea who had a furling headsail which had alternating tanbark and white sailcloth panels . He said the white was UV rotted but the tanbark was in good condition. You can see this on US flags in the tropics. The red is intact, while the white stripes are far more dammaged. Even that little bit of colour stops a significant amount of UV.
The problem is people mistake heat for UV. It is anything but. They are on opposite ends of the colour spectrum. Heat is infrared. UV is the opposite.
White polyester is not white fibres , the fibres are transparent, allowing UV to pass right thru, almost unhindered by any pigment. Any pigment or colour resists the passage of UV. That is why black plastic lasts far longer than white or clear, including in sail fibres.
The only increase in performance battens give a cruising boat is a slight increase in sail area, paid for by the loss of miles you get by having to go back to work to replace a batten damaged sail more often, while your battenless friends continue cruising..
Cruising standards for mainsails are set by those who have a huge financial stake in ensuring a steady supply of repair work, fixing sails damaged by battens, UV , etc. Those who question their disinformation live freer lives.
I have been cruising 11 months a year since my mid 20s. Those who let salesmen dictate their "standards " ( for their own personal financial embellishment) work the opposite way, work 11 months a year and take one off. Marinas are full of them.
For what my goals are ( freedom) I dont think I have been doing it all wrong .
You can judge the value of advice by taking a critical look at what it has done for the person offering it. Contrarians live contrary lives, contrary to spending most of it working.