I like some Airflo lines and heads, also Skagit heads for its performance and longevity. I got some dozens over the years, additional Guideline lines produced by Airflo.
I also have a lot of Rio
production lines and I am not at all label blind.
The problems you are describing, the relatively thick and stiff factory welded loops, I know all too well.
Solution for me from the beginning after purchase of another head:
Soak the first 5 mm of the loops in Aceton for a few seconds. Turn Fireline or Mono around each half of the loop and peel the coating off. Some turns of tying thread to cover the edges from coating to core. A cover of Aquasure or Stormsure around that and worked in into the core to protect it and at least this problem is solved. Try and get some experience in doing this on a couple of old lines...
I am tuning all my heads like this and it’s as smooth as can be with the loops inside the rings while stripping in. No need for an integrated line for me and on the run with full versatility.
But that’s a question of personal taste of course.
Another problem you described: stiffness of coating in cold conditions. Also well known to me with some of my Airflo heads.
The main problem seem to have their reasons in production tolerances. They are not only obvious in length and weight of heads with sometimes remarkable differences, but also in the coating. It can be different in suppleness versus stiffness.
Don’t be shy to talk to your dealer to get another head, independent of your further decisions. Airflo should get the feedback to do something about it.
If you have the chance to compare heads in a shop, maybe you could feel the differences. Maybe you are lucky to get the softest coating available for your needs.
And last but not least of course there would also be Rio