I've already stated my opinions on Victini being BL. Personally, I understand why it should be BL, but I think it adds a lot to the meta.
Many people argue that it lacks a definitive counter, but to be fair, it really depends on the set. Tbh, I would say the most used set (in my experience, I could be wrong), would be CB with Trick. If it runs u-turn, v, bolt strike, and trick, you can basically beat many bulky waters, such as megablastoise and milotic, as well as getting relatively free switch ins on like roserade, celebi, and florges. Trick allows it to beat things like crocune or maybe cm cresselia (if you are low on vcreates).
I think the hardest set to be would either be LO with coverage special moves + V-Create, or a lure set, with energy ball and glaciate. With these moves, you can beat almost every check to the physical set, such as quagsire, swampert, rhyperior, suicine, etc. The best counters would be things like CB/Vest/Lefties Snorlax, or specially defensive hippo. I've personally never had any issues with victini because it does not require a lot of scouting to see what type of moves victini has. It has the most potential the first one or two times it comes out. If you catch a swampert with energy ball, you are in the clear, but other things can easily beat it, such a healthy cune, or a mega blastoise, mega-amp. It reminds me of Kingdra in BW and Bw2, where it could be specs, dd, subdd, or rain dance.
imo it should stay. It is amazing at opening holes for certain mons, but it requires another mon to really do the cleaning up. ie something like v-create + special moves to lure in blissey/florges for something like subcm raikou to sweep. It isn't like lucario, which can effectively dismantle entire teams with SR and the ONE good answer to lucario at +2 (np/sd). I usually watch out for things like Lucario, as stated, as more of a threat because lucario is a danger to all teams, unless you carry like mega-aero + slowking + cobalion, or something like that to stop it cold.
+ things like banded intimdate krook, scarf hydra, duggy, they are all VERY viable mons, and they make victini's life a lot harder
just my opinions n_n