Poly is for wicking
Bike clothes, as well as some paddling and other sports clothes, are made to wick moisture away from your skin. Polyesters are woven to do that. I just use my long sleeve bike shirts and a light Polartech “sweater” as needed for layers.
Air temp
Wind blows right through a dry wetsuit. It is only useful if all the spaces in the suit are filled with water which stops the wind from penetrating. Even then, there isn’t much insulation as the suit drys up fairly quickly and it becomes much like a wet cotton t-shirt.
This is why I usually have a capilene shirt beneath my wetsuit. When surf fishing, I like to wade out into the surf and make my casts. There is no NEED to do that since I have plenty of range on my cast, but me…water…well, let’s just say I think my dad, being of Irish ancestry, was at least part selkie.
I found that a wetsuit alone didn’t work very well. The ocean is, on it’s best days, about 55F and the wind is pretty always there on the Ca. coast, so it dried out the wetsuit and penetrated pretty easily. Though I was able to get wet regularly, I did eventually become too cold for fishing.
So if the upper body is out of the water, and you intend to get wet, it is nice to have an insulating layer under the farmer john. If paddling in a full sleeve wetsuit, there are skin suits for wearing beneath the wetsuit that work well for this, also.
Rick