I did some testing with V2, and while it's certainly one of the better Attack options in BSC I wouldn't say it needs to be banned. I think that people are still a bit stuck in the Dual Layer era mindset that put way too much emphasis on the Layer of the combo, where you could get away with putting a more defensive Layer on a Stamina Driver and call it a "defense type" because Attack was played infrequently despite being in a relatively good state compared to Burst Standard nowadays.
Victory Valkyrie Knuckle Quick' vs. Wyvern Heavy Revolve
V2.K.Qc': 15 wins (9 KO, 6 Burst)
W.H.R: 5 wins (all OS)
V2.K.Qc' win rate: 75%
Victory Valkyrie Knuckle Quick' vs. Dark Deathscyther Gravity Defense
V2.K.Qc': 13 wins (5 KO, 8 Burst)
D2.G.D: 7 wins (all OS)
V2.K.Qc' win rate: 65%
^These two were considered top tier "defense" combos back in the day, but as you can see in figure A with a plastic Driver they can't really hold their ground against a rubber Dash Driver. I also did a benchmark against a pure Stamina combo to see how it compared:
Victory Valkyrie Knuckle Quick' vs. Acid Anubis Knuckle Revolve
V2.K.Qc': 17 wins (7 KO, 10 Burst)
A2.K.R: 3 wins (2 OS, 1 KO)
V2.K.Qc' win rate: 85%
Aside from one freak recoil KO, as long as I got the launch right V2 (for all of these tests, I omitted self-KOs or accidental tornado stalls) would almost always burst or KO A2. This also brings up the very real point that KO Attack is the most difficult type to use - in a tournament, this combo could easily lose 0-3 with 3 bad launches. So, even if V2 on X'/Hn'/Qc'/Jl' is a bit overpowered, it's balanced out to an extent by the skill cap required to use it.
Victory Valkyrie Knuckle Quick' vs. Unicrest Gravity Unite
V2.K.Qc': 7 wins (1 KO, 6 Burst)
U.G.U: 13 wins (all OS)
1 tie (double burst)
V2.K.Qc' win rate: 35%
Victory Valkyrie Knuckle Quick' vs. Gigant Gaia Gravity Keep
V2.K.Qc': 6 wins (3 KO, 3 Burst)
G2.G.Kp: 14 wins (11 OS, 2 KO, 1 Burst)
V2.K.Qc' win rate: 30%
I personally think that G2 outclasses K2 in every way, I also tried Neptune on Kp and it was alright so my options for KO Defense in Classic are a bit limited (Unicrest actually performed a lot better than I expected, until now I thought it was only melancholy defensively because I had only been using it on plastic Drivers), since I haven't had a chance to explore some of the Hasbro Layers that are supposedly really good for Defense (Evipero, Yegdrion Y2, Orpheus(?), and maybe a few others). But I think that once people adjust more of these combos will emerge.