Then that's nobody's fault but Jackman's. Logan is pretty steeped in tragedy and internal struggle. There's no reason he shouldn't be able to bring subtly to the performance. Instead, he does it as a pretty straight-forward tough guy.
I think you're probably basing your opinion of Wolverine's character purely on Jackman's portrayal of him--you're in a closed loop. If all you know of the character is the flawed performance in the films, then of course you don't think it allows for range.
The Japan storyline should require more of him, though.
(BTW, I DO think Jackman is a good actor...and honestly, I don't mind his portrayal of Logan---but it could be much, much deeper.)