I don't think thicker is the right word for the Griffins unless you're talking about the sole, there is very minimal padding on the Griffin, and the Howard is puffier. The Howard does seem like it would have much better board feel. I'm skating the my second pair of Griffins right now and they're great.
No disrespect intended, but the Howard is not puffy in any way imaginable. Puffy is probably the biggest antonym when describing the fit, design and construction of the Howard shoe. It's designed to fit as close to the foot and snug as could possibly be. The board feel is outrageous good.
And indeed, the vulc sole on the Griffin is much thicker than that of the XLK Howard. I have multiple pairs of both. As was posted a few pages back, the opening/throat of the Griffin seems much wider than the Howard and leaves more of the ankle exposed, where as the Howard 'wraps' around the foot and ankle and gives a much more stable feel.
EDIT: Both are really nice shoes, for distinctly different reasons. IMO, the Howard is one of the 3 best skate shoes currently available on the market from any shoe manu. And not for nothing, no other shoe company holds a candle to the functionality of the XLK sole. I thought about buying something out of Huf's catalog to show some love, but there is zero reason (for me) to skate in anything but Lakai. The Camby Mid is up next for me.