As said it really depends on what you're planning to do. Gravity riding can cover quite a few styles of riding.
If you're going to just ride the designated DH runs in Morzine/Les Gets (so runs like the French National, Canyon, Mont Chery, Plenny etc), then you can do those on Blur LT but I personally wouldn't find that much fun. I think you'd have to be pretty tasty to ride those runs competently and still have fun on a short(er) travel AM/trail bike. What will happen is that you will get really tired really quickly and end up being a passenger on your bike, rather than relaxed and in control.
If however, you're going to use the lifts to get you up to altitude and then do a days riding single track in the higher parts of the PPDS, perhaps head over to other locations like Champery, then the Blur LT would be great for that kind of thing. Your best bet, other than having a guide to take you out, is to buy a book on the AM trail routes in the region.
You can hire a DH bike out there, but they do tend to be beaten up and badly adjusted. Buying a DH bike is a big commitment and not something to just do on a whim. The better bet would be something like an Orange Alpine 160 or a Patriot or equivalent. You CAN ride those more readily on DH courses without it being a handful and you can still pedal them around a 50km day using the lifts. this is based on the fact that they are quite a different beast to a 140mm trail bike.