The problem with the games you mentioned is that they're niche titles at best, with Conker and Banjoo standing out among the rest by just a little. But with those titles being 3d platformers that have an art style that some may see as "kid friendly" will it really sell to the masses?
Well let us examine the list, shall we
MechAssault
MechWarrior
Crimson Skies
Kameo
Perfect Dark
Conker
Banjoo
1.) MechAssault was one of Xbox's highest scoring games of all-time. It set the standard for Xbox Live and provided a huge boost to the service in the days before Halo 2 redefined what it meant to play multiplayer on consoles. It sold over a million copies. As an Xbox Live launch game. Let that sink in.
2.) MechWarrior. Far from niche, the PC franchise spawned several releases. MechWarroir online F2P is certainly in the spirit of those games but not quite the same and suffers as a result.
All-time peak for that game was just north of 4,000 concurrent players. Not bad, but not what the brand was and is capable of.
3.) Crimson Skies was another of Microsoft's highest scoring exclusives of all time. It sold around a million copies. It was Warhawk before there was Warhawk. Considering how big Warhawk became for Sony, just imagine what Crimson Skies could have been if they had stuck with it?
4.) Kameo was perhaps closer to niche than any of the others, as I think it sold around 500,000 copies, but kept in context: it was a launch game for a platform that was supply-constrained. And while its gameplay wasn't as tight as it would have been under Nintendo's watchful eye, it was still quite enjoyable.
And who can forget that soundtrack. Games like Kameo serve an underserved audience on a platform that consequently allowed itself to be pigeon holed in a shooter and racing platform paradigm. Diversity is important on a platform for perception and to serve as many audiences with good content as possible. With roughly 500k in sales, there was more foundation to build off of than most games have, but seemingly not the will.
5.) The Perfect Dark franchise is somewhere north of 3 million in sales and its name is synonymous with FPS gaming as we know it today. It's a huge namesake. And while PDZ wasn't especially great, there's no reason to believe that a sequel in the hands of Rare or some other developer couldn't have build another million-seller.
6.) Conker and Banjoo speak to that same audience that Kameo speaks to. An underserved audience that would have been among the most avid supporters of the platform had such games received proper support. Both of those franchises are million-selling franchises and certainly not niche though Conker is a bit less traveled because of his potty mouth. Needless to say, when MS wants to they have no problem making a brand or character into a household name. Ask Master Chief, Cortana, etc.
So no, these aren't niche titles at all, let alone "at best". They are mostly million-selling franchises that had a strong brand behind them and more than enough potential to justify additional efforts and strong backings. Sony has backed worse game franchises for multiple generations (KillZone) yet Microsoft seems opposed to making sequels to games that were among the all-time highest scoring exclusives for their Xbox platform.
They had opportunities to make their own Zelda, maintain their own alternative to all the Sony-owned platformers, to have their own Warhawk/Starhawk, and to have their own truly unique FPS game (there really is nothing else like PD). Instead, they remain in purgatory or dead on the vine. And they have nobody to blame but themselves and their apparent unwillingness to put their full weight behind those franchises and their developers and
trust them execute their games without overbearing, "stifling" interference. So here we are.
$0.02
