The yield has been quite carefully though over, and for me it is ok. It depends on the 1. season, 2. knife, 3. timbercraft skill. Weight is not to be looked at anymore, as the relevant measure is the length of the strip.
You have to remember that bark from a standing tree is collected at height where you can reach, and it's not even possible to collect it as a long strip at very branchy section of the tree.
If we can come up with IRL reference that suggested that our measures are largely off then we'll adjust it. But just imagine how long strips you actually get, and they are inch or two wide. In reality, in the old times, bark harvesting birches were young with relatively small diameter - this isn't required in the game just yet, but the idea is there.