Don't know reasons to use AT oil that actually designed not for transfer cases
You admit you "don't know reason" why they call for AT fluid, and not gear oil.
I decided use thicker oil with more drag (and fuel consumption of course) to protect it from wear as much as I could
You decided thicker oil "would protect it"?
More drag = better protection?
How do you "know" the thicker oil is going where it needs to go?
If that's true, then why don't manufacturers just require 85w-140 (instead of 75w-90) in ALL differentials?
If "thicker oil" = "better protection".. then why not use gear oil in your engine?
Why do you suppose the design engineers call for ATF (over gear oil) in transfer case?
Could there be reasons you don't know?
Personally I can't say that it will be catastrophic or not... but I'd certainly be cautious without "knowing" why they call for ATF.
Not all mods are bad.. and you have decided your reasons.
If you're wrong, you admit you'll wait and see, and live with it.
It's fine to vary from popular consensus.. but sometimes there are reasons.
Sidenote: A few years back.. I got caught up on some 4x4 forum site that was calling for modifying your power-steering pressure valve for more pressure (to presumably turn bigger wheels). What wasn't known is that increasing pressure also increases heat and wear. My fluid was foaming and it caused me a great deal of trouble when my power-steering became jerky and failed. I went back to what the engineers designed, and it now works as it should.
It's fine to make an "educated decision".. and if you feel that your mod is better than what the actual engineers designed.. then go for it.