If you are a paid event photographer, I would go for the 7D2 for the following reasons -
1. Dual card slot data integrity. It isn't a matter of IF, but a matter of WHEN a card will fail. You can't reshoot an event. Many data recoveries succeed, but NOT ALL. Of those that succeed, rarely are 100% of the photos recovered. After all, the whole reason a failure took place is because data on the card became corrupted. In this day and age of social networking - reputations can be ruined quickly and hard earned referrals lost. Ignore all the morons who will say this isn't that important. If that was true, the 5D and 1D series would have one slot, but they don't. You owe it to yourself, your business and the customer to protect the images. The 7D2 does that at a very reasonable price point. It is almost unethical not to.
2. You said video, 7D2 has good video. The 6D does not. 7D2 lacks only the articulating touch screen. If you do video that requires that, then you really need a 70D and set that up as a dedicated video rig and forget trying to do it all in one body because you give up too many other things going with the 70D.
3. Speed. Events often require a decent FPS to capture key moments. At 10 FPS, the 7D2 will do it. The 6D has a lousy 4.5 which means you and your finger need to have good timing.
4. AF system. Depending what you shoot during these events, the AF on the 7D2 is better.
5. Build quality - the 7D2 is tougher.
6. Anti-flicker. This feature alone is worth it. Events are often take place under crappy fluorescent lighting. The anti-flicker mode will dramatically reduce your post-processing work flow and improve consistency across the album you create.
7. 100% finder on the 7D2.
The only things the 6D does better:
1. Sharper, better image quality all around. FF advantage here. FF sensor will resolve more detail even at the same megapixel count. Not much else to say.
2. Better low light performance. If you genuinely run into situations where you are shooting at ISO 6400 and 12800 AND using these photos as keepers - the 6D will show an improvement. At lower ISOs with NR, it makes little to no difference on print. Some would rightfully argue the 7D2's ISO 6400 shots are perfectly usable, and they would be correct. But that depends on your standards.
3. DOF. Again, FF advantage here. While APS-C can be wonderful, all things being equal, the FF sensor gets a perspective the APS-C cannot. Although, in event shooting and to customers - I doubt they would ever notice or even care. Good glass is a larger part of the equation.
I would easily weight the 7D2's advantages as much more important. There are tons of pros out there shooting 60D, 70D, 7D, 7D2, and even the 40D!....the image quality as you already know, is perfectly fine. Results are great, and you can create albums, prints and slideshows and whatever that easily meets typical pro standards out there for albums.
If someone said they just shoot portrait sessions, the 6D is the easy choice because that is a controlled environment and all the 7D2 advantages no longer matter. You control the pace. You can reshoot (within reason). You can tether or wifi transfer. You control the lighting. You focus where you want every time. All the difficulties of event shooting vanish - and all you are left with is which camera has better image quality. That would be the 6D.
However, in the real world things are really tough at events, the 7D2 has features that really do assist in making the shots. There's little time for adjustments. Things happen quickly. Conditions are never ideal, and often they are awful. The 6D shoots like an older DSLR.