Firstly, you're using a kind of straw man - that this stuff is "nonsense." Now you may not like it, but you should at least acknowledge that some people will actually really enjoy it. We happen to know this for a fact. And there's still a possibility, that you might actually enjoy this new stuff, or that it will simply fade from your area of botherment.
You should also acknowledge the following - that the MP has performed incredibly well in large scale and focused testing, and that many different constituents have reported excellent experiences, including pro and competitive players, even in the new stuff. This is hard empirical data, not us thinking Bravo smiled three times in a game of Infinity Slayer, but acres and acres of intensive test metrics and reports.
Secondly, the addition of lots of new players will provide many, many general improvements - better hosts, more player skill ranges, better banding and matching of players by skill and interest - even if those players are like you and presumably want a more stripped down experience. All boats rise of the tide.
Will it be perfect? No of course not, it's 2012 and Halo has too many types of player to make absolutely everyone perfectly happy, but that's an impossible task anyway. Our job is to make a game that appeals broadly AND deeply and to give players tools and varieties of experience that get as close to those ideals of taste and style as possible.
Thirdly, the logic of making a very narrowly focused game at the exclusion of all else would obviously be something that's managable at an Indie level, or as a PC game, but the reality of making a AAA console game, and the reality of a constantly evolving and growing Halo, is that it cannot be created as a niche game. However, it does contain niche ingredients and tools, within the very very broad suite of features and play experiences. You can in fact have your cake and eat it. But the idea that more players is bad, or that the core game is being dumbed down, is erroneous.
/SaturdayMorningSalt