Ventile requires re-proofing though, no? It’s not like a magical variant of cotton, it’s just cotton with treatment.

With the margin of error in the outdoord being as small as it is, I’d trust synthetics or wool that will always work vs the risk my cotton isn’t treated recently and reaches failure.

On the contrary, Ventile should never be proofed. PFAS and such were used earlier as a lubricant in the textile mills, but is now replaced with something more eco-friendly. The water-repellant properties of this was something akin to a happy accident. Original WW2-era Ventile did not use this, as you might guess.

Ventile works it's magic by the combination of long fibered cotton, thigtly spun thread and a close weave. The result is a fabric that after some time swells in rain by absorbing water, and then becoming saturated and impermeable(ish) to further ingress of the wet stuff. The inside will feel damp, but not wet. Wool as a base layer is of course an excellent counter to this. And, all the while excess body heat is shed quite effectively. When at rest, put on a wool or fleece 2nd layer, just like with a synthetic shell.

A compromise, yes. But the greatest advantage over 3L membrane etc. in my opinion is the ruggedness and durability, "experienced wetness" beeing alike. And in the high mountains, boreal or a mid-winter climate with months of stable sub-freezing tempratures, this is a supreme choice for your outer shell. Sweat converted to frost forms on the outside of the garment, instead of the inside as it is want to do in a 2L or 3L. Brush it right of, and carry on.