Involvement in attack is not something I'd measure solely on assists, even if you can't deny the numbers. And much more important for me, is the balance your wingbacks provide. Knowing when to attack & knowing when not to, securing as much of their side as possible, being available out wide to spread play,...
For me, Asamoah is close to excellent in that regard. Which means I couldn't care less if he was a true LB, CF, CM or GK. In other words, if Asamoah is better at this job than 95% of the so called true LB's out there, is this then not also his position?