So I read the Mouse and Keyboard post on the front page of CPB earlier today and if I can, I want to address the arguments put forward by people like Lupo (but not just him), when they state that a Mouse and Keyboard does not provide significant advantages over a controller.
First and foremost, let me state the obvious. Using a Mouse and Keyboard will not make you into some aim-bot like God where you will win every single PvP engagement you ever come across; nothing but actual skill will help with that. That said, a Mouse and Keyboard does inflate your skill by providing you with significant advantages that controllers players just don't have (or if they do have these advantages, like being able to play on max sensitivity but keep deadly accurate aim, it certainly takes that person a lot of time and effort to get good at when compared to a Mouse and Keyboard player).
Secondly, in the effort of full disclosure and to give my post some context, I used a Mouse and Keyboard for Destiny PvP for the better part of a year, because it absolutely provided me with advantages that controllers couldn't. I was a scrub for lack of a better term - I had a wife (and kid coming on the way), and between family and work, I'd usually only get time to play PvP for an hour or two every other night on Destiny. No excuses though, I was bad at the game and wanted a leg up on others - something which I came to realise over time, was wrong and actually lessened my enjoyment of the game. What a Mouse and Keyboard did was immediately increase my 'skill' over most Destiny PvP players (who use controllers), as I was able to do things they couldn't. That's not to say I didn't get my ass beat in PvP every now and then, as I absolutely did, but these were from people who had put in serious time and effort to get good at PvP/Destiny (i.e. they had a 100k or more kills in Crucible, 50 DTRs across the board, and high K/D and W/L ratios etc).
Now, the main arguments you hear for why Mouse and Keyboard isn't as advantageous on Destiny is that the game is 'special', in that it is somehow more tuned for controllers than other console FPS games. Whilst that is true to some degree (as a game like CoD is certainly a bit more Mouse and Keyboard friendly than Destiny), the fact of the matter is, a Mouse and Keyboard STILL allows one to play on a 10 sensitivity and yet still maintain incredibly accurate aim. Yes, Destiny (as with every other console FPS) has turn limits built-in that you absolutely cannot get around no matter what peripheral you use, but this can be mitigated by a large degree with curves you can create using the manager device. With some time and curving experience, you can create some seriously nasty movement and aiming curves to help fine-tune things.
There were also some arguments made recently that one cannot change sensitivities with a Mouse and Keyboard, and this too is wrong. Whilst you have a separate HIP and ADS sensitivity, you can also toggle these sensitivities higher/lower depending on if you are using a Shotgun or Sniper for example, all with the press of a button. In game (i.e. on the Destiny sensitivity menu), your sensitivity will always remain on 10, but with a Mouse and Keyboard you can manipulate sensitivity depending on what weapon you are using incredibly easily (not to mention toggle different DPI settings on the fly depending on what mouse you are using).
Finally and with all of this said, here is where I'm at now. I stopped playing on a Mouse and Keyboard in November 2015, as it honestly felt cheap - when I'd win gunfights, I was never happy with my performance, as in the back of my mind I knew the reason I won a certain gunfight was very likely down to me using a Mouse and Keyboard and my opponent using a controller. I've switched to the latter now, and whilst I'm certainly not as good as I was in my hey-day using a Mouse and Keyboard, I'm just happier when I play PvP now (i.e. when I win a gunfight, I know it was down to my skill so to speak and brings some modicum of pride when I can see I'm improving in the Crucible).
I also want to mention that I have no ill-will or malice towards Lupo himself; indeed, as someone who just had my first daughter born recently, I wish Lupo and his family the best. That said, I find the use of Mouse and Keyboard in PvP to be beyond ridiculous/cheap and it just brings a bad-taste to my mouth to put it lightly. Indeed, if Destiny does ever get a competitive scene, you can be damn sure that Mouse and Keyboard won't be allowed on console tournaments (just look at the main CoD or Halo tournaments, which is the best comparison we have of professional console FPS e-sports).
TLDR: Using a Mouse and Keyboard is not an instant-win button, but it undoubtedly provides a huge advantage over controllers. Mouse and Keyboard players are being disingenuous with the community if they cannot own up to this in my experience.