There is a good deal of information in this very thread.Could be. Then I would be interested in some solid writing on the characteristics of linen and comparison to cotton.
The faulty information is contained here: "Personally, I advise against linen. Yes, it is light and it absorbs water like a sponge; unless you are wearing a revolutionary deodorant, you will spend the day with marks under the arms as soon as you break into a sweat."
Good quality linen shirting is not light. It is heavy and much heavier than most cottons. I think the error in the writer's judgement stem from a lack of experience and knowledge of the subject being treated (that elicited Concordia's pertinent remark.) The only shirting linen that is light is defective linen, the kind we would not even think about making into bespoke shirts. A lightweight linen woven in who knows where would perform no better than an average cotton.
Good thick Irish shirting linen, absorbs moisture, but as it is thick it can absorb a good deal without leaving any marks (never had them, ever, and that includes brutally hot Sicilian days.) The absorbed moisture not only leaves no marks, but actually acts to cool the wearer. The slightest bit of a breeze is refreshing.
Cotton is the most uncomfortable choice on a hot steamy day. And inferior quality linen is only slightly better.
The most "solid" information you can get is to make up a good quality linen yourself and give it a try. Do it.
Cheers