I think it's a mistake to get hung up in the percentages, or whether it's a wild trout or a hatchery trout. The point is that air is bad for them, and exhaustion is bad for them.

The logical conclusion, in my opinion is,

a) don't bring them into the air, at all.

b) use gear that can control the fish rapidly. 4 lb test kills steelhead. I never use less than 8 lb.

c) use a net. You can net a fish more quickly than you can tail a fish.

I know that netting is controversial. This past year, I caught and released the same fish (steelhead) pver a three week period three times. On the third time, he showed no apparent damage, despite having enduring a nylon net. He never left the water, and was released quickly.