I am happy to recommend this too, but don’t be fooled into thinking the decathlon stuff is anyway as breathable as the branded gear.
I never said they are equal and the recent price increases make them less of a good deal. When they were 60 and 30 in sales, they were the best proper 3 layer (not 2 or 2.5 like many of the suggested alternatives) jackets with pit zips you could buy for the money. Buying two or three for the price of one jacket elsewhere was hard to beat! The lack of some MTB specific niceties and marginal difference, in on paper performance (I found no discernible breathability difference compared to a Madison Addict or Berghaus, forgot the model name) was not a massive gulf unlike the prices!
Breathability claims are both exaggerated and academic at best. In the real world they’re subject to internal and external environmental variations that severely reduce any of the manufactures claims, that MAY be provable in lab conditions. Comfort seems to be more to do with the layers people wear underneath (varies a lot), a persons effort/amount of perspiration, amount of ventilation and how arduous the conditions are. Not to mention good fit and any wear (dirt and abrasion) issues from use. Get any of them constantly saturated, with you putting in some serious effort, close to freezing conditions and any breathability goes out of the window altogether.
BTW not tried the AM Jacket. There are other 3 layer jackets from the hiking range, slim fitting and good enough for MTB. If the price isn’t right don’t buy!