MS first party, in my opinion, has been very mediocre compared to the standard they set at the beginning of last gen. Halo 5 sold worse, and scored worse than 3. Forza has become NFS releasing every year. Fable has gone pay to win or free to play, I forgot the genre. The Gears Remaster didn't even chart for NPD. Their core franchises are on a downward trajectory and the new ones they're building are being made by third party (Remedy, Platinum, Armature) which is risky because there's no guarantee the studio (or the game) will stay exclusive. MS no longer has that huge US/UK install base to guarantee them sales for basically any game they market out i.e. Tomb Raider. I would not say they are doing very well, they are getting trounced by their competition and they know it.
I do agree their output has been mediocre, but you are intentionally only focusing on the negatives.
Halo 3 sold better because it released during Halo's and FPSs hayday, being the trilogy finale of one of the biggest franchises in gaming. Fable hasn't "gone free-to-play", they are simply making one singular installment in the Fable IP that is a MOBA. A franchise may dip into many genres.
GoW: UE charted at NPD, and sold over a million copies, which is very good for a low budget remaster.
Forza Horizon and Motorsport are two different types of racing games simply sharing the Forza name, that all review great.
News flash: Sony and Nintendo also develops exclusive content by third-parties all the time. So was Gears of War, until MS now decided to bring it in house.
MS also owns the IPs for Quantum Break, SCALEBOUND, Cuphead, ReCore, Ori.
And yes, Playstation is trouncing Xbox, but how i that relevant to their first party output? And they may still be doing well even if someone else is doing better.
Tl;dr: I agree that MS's core franchise have lost impact, perhaps even quality, but your reasons for why MS has a mediocre output is all over the place, and it's obvious you're grasping. You may not like Sunset Overdrive, Ori, Ryse, DR3, or any of the core franchises, but it's not all bad. And 2016 is looking great.