IMO 22 inch is a compromise, longer barrels make a more efficient use of the .308 potential, along with other calibers. It is likely the amount of unburned powder can be quantified and represented as a percentage. Certainly, a faster burning powder could be used, but chamber pressure is the limiting factor. It is all a compromise. But to gain the best efficiency and possibly accuracy, from what you have a 16 inch barrel seems like an unlikely candidate for the .308. I guess ergonomics may be the overriding factor for using shorter barrels, inside a vehicle, inside an airplane, close combat dedicated, or for a more compact rifle with a suppressor mounted.
Side note when they designed the M-73, one of the larger pieces of crapola ever designed, it was designed to fit in the available space on an armored vehicle. Even with the space restrictions, it was made with a 22 inch barrel. I doubt that number was pulled out of someones rectum, likely numerous criteria were considered. M-60 machine gun 22 inch barrel, M-14 rifle 22 inch barrel. I personally think the trend towards shorter barrels is style-driven and not function-driven. IMO if you have the need for a short barrel go for it, if not why not opt for practicality, function over form.

This, exactly.

Out of over a hundred rifles I own, only two of them are 22”, one of which is my least favorite rifle, edging itself off of the chopping block closer every day. From 7” barrels to 31”, function over form. There’s nothing I do which dictates a 22” barrel as optimum. The ocean is wide and deep, go exploring!

I love my 20" PA10. It is very capable. That said if I were to do it all again I'd get the 6.5 chambering.
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ID skip over the tech, reasons here and just say that I've hunted for decades with a hunting buddy that has had a job for over 20 years as,
a swat member and now recently due to age, a police trainer now that hes older and hes hunted with a 308 synthetic stock carbine with a 22 inch barrel
and a 165 grain bullet, he built, to use in swat team, completion's, simply because its exceptionally accurate and effective.
hes taken a few decent mule deer and one elk that I know of and has had zero issues
remember its not the cartridge you select or use that determines your success,
as much as the skill and experience of the individual using the rifle and his understanding,
of the strengths and limitations of his weapon of choice.
youll be fine with a well thought out 308, but personally Id suggest a 20"-22" barrel to come closer to maximizing the cartridges full potential