Just a few thoughts to make you less nervous about riding a CF fork. Not trying to change your preference for material. I actually prefer metal frames over CF too, but not because CF is unsafe. OK, here goes:
Yes, CF can make designed to be very thin and light, but the same goes for steel. What you and I might say is "too thin, too light" is just what someone else wants to buy. High-tensile steel at 0.3mm wall thickness has to be manufactured to high quality standards and handled carefully to be strong and safe.
Degradation of CF due to heat, humidity and UV exposure is a concern for aircraft, but unless you have to store the bike outside in the sun, I wouldn't worry about it.
Good you are learning to trust CF. Anyone riding a CF fork needs to have trust in CF, the fork being critical to safety. I've seen a guy ride with a failed chainstay weld (on a cheap Fuji al frame) and barely notice, but having a fork leg separate is a whole different thing. The bending loads on forks are extreme (potholes, limit braking with 100% weight on the front wheel) yet high-quality CF forks have proven to be up to the job.
Not sure what you're talking about with the stiffness. Stiff and strong is good. Going to a high-tensile newer aluminum alloy such as 7075 T6 allows for triple-butted tubes to be made lighter and stiffer than 1950's era metal...that's good.
I've got a custom frame from 2003 made from Columbus Zonal megatubes with a CF rear triangle and Reynolds Ouzo Pro fork. I rode it for 13 years, 40K miles, including lots of hard climbing, with no evidence of any problems.
So, I'd say don't worry about your frame materials. Pay attention to any noises or flexing, inspect carefully after any big impacts, and go ride.