Why would we compare the 338LM to the 308? They are two entirely different classes.
Because the question was posed about the short barrel defeating the purpose of the cartridge. I made the comparison because these standard .308 loads are widely considered suitable for targets up to 800 yards (and beyond for many users).
The .338LM even with a 20" barrel far exceeds the capabilities of the standard and most common long range precision cartridge so it purpose is certainly not defeated.
I was stating its superiority based primarily on drop and wind drift, but there is also a very serious upgrade in down range energy and penetration. Again the short barreled .338 serves a real purpose.
I agree the .308 and .338LM are in two entirely different classes.