yes, but it is hard to get out 3 Lv.X. Blissey works faster to beat AMU when it is Speed Blissey. I think that Blissey Speed with no boosts but maxed Buck's Training, Pluspower, and the Happy Chance attack can take out any deck. Adding Rare Candies could make it good too for turn 2 or even faster attacking. That way, you can add in Stage 2 techs like Empoleon MD so that you can Dual Splash the bench. After this, they bring out their bench with damage already so Blissey needs less energies to attack and more time to power up benched ones.
I tried Blissey Speed and it works out good with proxied rare candies. I got 3 t2 Blissey out of 5, which is great.
The match-up after the rotation in September will be in Blisseys' favor becasue no good Fighting Pokemon will be played with AMU and Kingdra. It will come back as a new archtype, and many LA cards like Kingdra combo with it. Even Blissvire works with like 4 Switch so that you can Happy Chanceand move the Energies around to do about 60-120 a turn. Blissey is too big of a tank to miss out on.