Lewis's jab is good but he paws with it. Sure he's used his left with reasonable effectiveness, but he's struggled against guys that can get their timing and distance and jab back. Ray Mercer, for instance, gave him fits with his jab when they fought a rather competitive bout. When the guy can't get close, Lewis will jab or, even worse post out. He indeed has power, but usually his jab looked its best when he was throwing it into guys that would stand in front of him. Tua, for example. A slower, older Holyfield was hit with it, but in the rematch, it was less effective when a more invigorated version of Holyfield showed up.
Wlad moves reasonably well, left and right too, times a strong jab (and when he strings a right hand behind it, can be downright destructive), and avoids putting himself in bad spots. Lewis won't have such an easy time. What made Vitali lose was his willingness to brawl, this gave Lewis openings. Wlad is a very sharp puncher. He's a big guy, and even if it can be conceded that Lewis is on the same level as Wlad with the jab (I'm not wholly convinced of this), Wlad moves well enough to turn Lewis, and Lewis will have to be more aggressive than he perhaps might like to be.
I'm not saying it's an open and shut case here. It's interesting, but not something so easy to write off..