Mw13, I had though of that argument, but didn’t make it because it’s more complex than that.
Say two people gave you a ride (equal distances) on two separate occasions. Say Reuven was going there anyhow, but Shimon had to go out of his way and perhaps alter his schedule. Wouldn’t you owe more hakaras hatov to Shimon?
OTOH, say they expended the same effort, but one was a ride to the grocery, and one was a ride to your own child’s chasunah which you would had otherwise missed. Wouldn’t you owe more to one who gave you a ride to the chasunah?
Both the effort and your benefit factor in to how much hakaras hatov you owe. True, we owe Hashem infinite hakaras hatov despite His not incurring a loss, because everything we have is from Him, but that doesn’t mean when it comes to human beings effort doesn’t matter.
In reality, comparing hakaras hatov owed to lomdei Torah to that owed to soldiers is comparing apples to oranges.
You could perhaps argue that the benefit from the lomdei Torah outweighs the more literal mesiras nefesh of the soldiers, but in no way can you discount the mesiras nefesh of the soldiers in appreciating them.