Hey there.
I have taken the liberty of making some gifs to show the difference between the Silithidtank/Qiraji Battle Tank model and skeleton, and that of the Ravager2mount, aka Grinning Reaver skeleton and model. So without any further ado, I will go ahead and list the animation gifs here.
Ravager2mount animations:
Bonus standing animation: http://i.minus.com/ibvqhIhb5YgMka.gif (completely unique. Silithid doesn't have it.)
Walking animation: http://i.minus.com/iliUgsqyS1gum.gif (for the most part, old. But modified to be smoother)
Running animation: http://i.minus.com/ib1lK4VXr2GvUo.gif (same. There is a difference, though. You'll see.)
Battleroar animation: http://i.minus.com/iUyitwOFgIgFY.gif (same. Could be modified to be smoother.)
Death animation: http://i.minus.com/igCuTbvy40jPO.gif (same, but looks more graceful in my eyes; probably modified)
Flightidle animation: http://i.minus.com/ibwWkrpgY1Lx1h.gif (obviously, completely new)
Flightrun animation: http://i.minus.com/ib0b8qeEebTtxc.gif (also obviously new)
Swimming animation: http://i.minus.com/iJEFmfgzvLequ.gif (general animation is same but smoother + wing and mandible anim.)
Attack animation: http://i.minus.com/iH9TROMwTUUIT.gif (similar principle as silithid attack, but certainly different animation. That much is obvious.)
Silithid animations:
Bonus standing animation: http://i.minus.com/ibrMJFsAG4ZLST.gif
Walking animation: http://i.minus.com/ibxHeqbBAROEmp.gif (face down, ass down. Less smooth, seems to slide rather than walk)
Running animation: http://i.minus.com/ibd0ffVebgBkh6.gif (less smooth, seems to glide across ground, not run)
Battleroar animation: http://i.minus.com/iNq0yyHrCjam1.gif
Death animation: http://i.minus.com/ice8Xfj6aUZhw.gif
Swimming animation: http://i.minus.com/ibnaNxEoV1Tcnm.gif
Attack animation 1: http://i.minus.com/iLUp2fKi4NdOK.gif
Attack animation 2: http://i.minus.com/iDESsJ4K700lb.gif
Conclusion:
Claims of "lazy" are completely unfounded and unfair. This new ravager mount is not a literal skeletal copy-paste with a new model. Even if it was, that would have been a big job. But it is the second largest and second most intensive/extensive task for 3D artists that was involved here. No, they didn't grab a new skeleton because they knew it had to behave roughly like an already existing creature does (the silithid), but they also certainly didn't just stuff a silithid skeleton on to the model and call it a day. Like the Pterodactyl mount that they created using the Proto-drake mount skeleton as base, they modified existing animations to be less choppy, more lively and well-animated, and added new animations altogether in many cases. Of course that is obvious for the flying, but there are also other new animations.
Case in point: the running is similar, but there is no way it wasn't modified. The silithid's animation isn't particularly great compared to the ravager's. You can see the ravager actually set the steps, while the silithid glides across the ground. Not that I'm trying to bash the animators of that time because WoW was different then, and the models were of lesser quality for good reasons, not because the animators and modelers were bad.
In summary: think before you hit that reply button and accuse Blizzard of "lol just lazy reskin lololo blizzard selling out".