BC is definitely important. PC gamers can go back and play any old game they so desire. They don't have to keep their old PC or pay a company a monthly fee to stream their game to be able to play them, they just can and with no extra fees and with a higher fidelity. This is what Microsoft is building with the Xbox right now, and you can bet that with a team of 100 strong they are not putting in all of this work for nothing; the next console will support all form of BC back to the original Xbox, I'd bet anything on that. People play older games all the time. I don't think that releasing Shadow of the Collossus for the third time with slightly better graphics and making people pay 60$ again is old for your player base wen they could have a similar solution to MS's and have it natively rendered in 4k on their PS4 Pro for no extra cost to owners of the original.
You also have older games selling out on amazon, prices skyrocketing or getting in the top 10 most played games on Xbox Live when they launch on BC. And it's not because of a lack of games to play, it's because people genuinely still care for older games and don't want to keep 10 consoles plugged into their TV to play all of them. If BC wasn't a thing I can honestly say I wouldn't play any of the free 360 games I get every month, as I bet most people don't with their free PS3 games as they don't run on PS4. But my Xbox One X runs them, so I've been playing more 360 games regularly because it makes it easy for me to do so. And by they way, Ninja Gaiden renders in 4k on Xbox One X, something even the PS3 version wouldn't be able to do and the extra bells and whistles it has doesn't make it look better than the 4k version I am playing right now!
The generation was decided in the first few months because of the price and power gap. Even when they reached price parity, PS4 was still more powerful and the word of mouth had already gotten out. To think exclusives had anything to do with it is foolish and downright stupid. And all of the exclusives they are getting (like Nier for example) without any deals is because of that momentum. The player baseball is bigger on PS4 so the risks are smaller to take there than on Xbox right now. It's not because MS isn't putting in the work, but there is no way they could be paying for all of those games to come out on Xbox One when Sony isn't.
Also, this is my opinion, but yes, Halo, Forza and Gears are a lot more compelling than any Sony franchises releasing this year. When I pay 60$ for a game, not only do I get a single player story just as long as your Sony games, but after 10 hours wen the campaign is over, I can still spend hundreds of hours on MP, getting much more value out of my game. With God of War, after 10 hours the game ends up on the shelf and gathers dust as there is nothing else to do with it. This is what people want and also why free to play is so huge right now, because we get value out of it.
Maybe some of you guys should go here:
https://www.microsoft.com/en-ca/store/most-played/games/xbox and see what people actually play. You'll see most of them are multiplayer driven. Then go here :
http://steamcharts.com/top and do the same thing, you will get the same result. Reason is because multiplayer driven games are where it's at right now.
I would never buy a console because it has a longer list of exclusives I'll never play anyway. I buy a console because it offers the best overall experience (Xbox Live, graphical fidelity, BC). People don't buy PS4 for exclusives, they buy it because at the 200$ price point (which is what most people will pay), PS4 is the most powerful out of the 2 and has the momentum. PS4 Pro and Xbox One X are only a drop in the bucket and we all know it. So if you take out the casuals who are most likely getting the PS4 because of the reasons I already listed or maybe the more informed ones who prefer their Sony games, the reason why some people are still buying Xbox One S over a PS4 is the more informed gamer who either prefers MS exclusives, 4K blu-ray, controller, online infrastructure, friends, etc and don't mind playing at 900p instead of 1080p.
But for the mainstream people, most will usually go with a PS4, and it's not for the exclusives. And MS has no appeal outside of US and UK, so that widens the gap a lot more. Because here in Canada, all the people I know that still play on console are mostly on Xbox One, and I didn't need to threaten them to buy one, they did it on their own!