The difference being Tua kept coming forward and launching hayemakers. Even though he was physically out matched and technically out classed. He tagged Lewis with a few and kept him on the back foot the whole match and made Lewis move and use his reach. I think Lewis was far more active with his right hand against Tua than Wlad would be in a similar situation. Tua v Lewis was a way better fight in a lot of ways, even though it was a one sided result.
One last thing, it's not that Wlad was even dominant last night, he was tentative as well, he just happened to be more active than Haye.
Lewis vs. Tua was a totally different fight, and one in which Lewis boxed beautifully and landed numerous power punches flush. There is really no comparison between the skill sets of Lewis and Vlad - Lewis was a far better fighter in all respects.