about the 'plastic bag' comparison, my impression from the YKYWB and Darevie clothings is that the fabric is well-ventilated and wicks the moisture pretty well. For jerseys especially, and I even have one from YKYWB which is summer specific, and has a mesh fabric for the whole back and sleeves, which is really cool and fit for hot rides
But for bibs also, I don't have any issues with them being too hot (currently have 4 from YKYWB and 3 from Darevie), not even for indoor rides. But surprisingly they also hold the heat well in the coldest rides.
I cannot compare to Spexcel bibs since I have none. But the 3 jerseys I have from Spexcel, my impression is the fabric is hotter, slightly.
I think it has a lot to do with the material/lycra used.
I have a Spexcel jersey with their coldblack lycra and I will happily wear on stupidly hot days aka 35C+ it is one of my better jerseys for wicking sweat away (and I do sweat a lot).
I have half a dozen YKYWB jerseys, don't find them that good at wicking moisture away (I have better alternatives) so they get used on the normal 15-30C ride days.
My only experience with a Darevie jersey (long sleeve) was not positive.
With regards to bibs, I find the lycra in my Spexcel and four Darevie bibs to be lighter, less compressive than other bibs, but good at wicking sweat. Will happily use them on hotter days as long as the ride is less than 4 hours.
My YKYWB bibs are black cargo bibs, don't wear tend to wear them on hot days.
