1) You are breaking IP Laws if you are trying to take an existing game and modify it. Taking the general concept of the game, minus gameplay elements that have been patented (not many of those exists, but they do exist), and creating a new game with original art, story and names is fine. Using the name, the art or the un-modified story of the original game is not.
Keep that in mind when thinking "I could make this game MUUUCH better!".... even if you could, you should make your own game inspired by the other game, not the other game plus your improvements.
2) As Tom said. You will not be successfull pitching to devs. You need money to pay devs. If you have the money, you don't need to pitch to them. You CAN try to pitch to publishers, though I don't think you have much of a chance any of them will listen to you, no less if you try to pitch an MMO now (every publisher must have 3 or so failed or dying MMOs in their cellar by now... nobody REALLY wants to waste money on MMOs anymore).
3) An MMO is expensive as hell, and takes an incredible amount of manhours to build. Depends on the MMO in question of course (building a mobile MMO client is of course much cheaper than a PC AAA MMO Client, and the backend might also be a little bit cheaper because of simpler gameplay and all), but generally, you are looking into the 10+ million $ realm at least, with AAA MMOs being 100+ million $, and very expensive to run for anything above 1000 concurrent users.
Are you sure your pitch is good enough to make ANY publisher reach for their wallet to give you a budget for it (even if there are still publishers interested in MMOs)?
If you have the money to pay developers, are you sure your game idea is good enough to sink this much cash into an game that is most likely going to fail in the market (in this case, if you pay 100 million for development, and servercost + marketing make for another 100 million, anything under 200 million $ profit is failure)?
4) If you pitch to a publisher, you will no longer be in charge. Sure, if you are a person with a name like Carmack, or Mollineux, or Sid Meier, you might pitch an idea AND get the position as the lead for the project. Still, the publisher owns the game now, not you as the lead. They will let you do your thing as long as you follow their guidelines and your name still has value for them.
They will kick you from the project as soon as they feel you no longer share THEIR vision.
The only way to really be in charge of something is if you have the money to pay for the WHOLE shebang. If you are a millionaire, you can be in charge.