Which have you played from their work? KI is mediocre? How so?

I doubt he's played KI (because its amazing), but on the other side of the coin, the true credit needs to be given to the outside devs, not really to Rare. They kind of made lemonade with Microsoft and Rares property. 

Don't care about who made it at all. Seriously. The game is amazing regardless.

Hence the point. The games merit is in the value it brings, plain and simple. It just adds to the value of the Xbox One library.

Of the MS Rare games I've played Viva Pinata, and Perfect Dark: Zero (duh), Killer Instinct (more on that in a moment), Nuts & Bolts, and season two of Kinect Sports.

This is going to sound weird, but I have the same issue with Killer Instict that I have with Resistance. Everytime I got done playing Resistance I walked away thinking "Well, that was certainly a  first person shooter". Killer Instict in certainly a fighting game...but that's really it. It's just missing something, it's not as tight or as out right fun as a game like MKX but it's also not as hard edged or challenging as a game like Street Fighter or Guilty Gear. The combo and special system is pretty neat, but the actual fighting itself is only meh and the roster is sub-par.

I think it is pretty obvious why they aren't in

However, while Goldeneye was praised when it first came out, it has aged horribly, DK on the other is still great today

Goldeneye really has aged pretty badly, and DK is owned by Nintendo so that couldn't be in it...still, it would have been sweet.

Ok cool. I've heard one of their better games was Kameo. I'll play it when I get the collection. I didn't like Viva Pinata although, admittedly, I didn't give it a fair shake. Kinect Sports were good showcase games. I liked them.

Killer Instinct is one of my favorite games. I feel the roster is very good and diverse. It's just getting back in the swing of things after being dormant. SF MK and such have consistently been around for decades. It's very good and obviously I don't agree with some of what you said about it.

If Rare was so great wouldn't Nintendo have kept them? Why were they even for sale? 

See I think the thing that has aged badly is the controls. The rest of the gameplay I can imagine being still quite good. Redone controls and there is still some merit to the goldeneye gameplay style imo

There seems to be two sides with Nuts and Bolts. People that wanted a traditional Banjo game hate it. Those of us that think the original Banjo games sucked like Nuts and Bolts. It also depends how much you like building stuff to complete missions. Bottom line, for that type of game its great.

Kinect Sports Rivals was solid for a motion party game. Again, it just depends on your interest in that type of game. I had more fun Kinect Sports than most Rare games.

KI 1 and 2 are well above mediocre. Especially if you actually know how to play them. That series was very popular and there was demand for more.