If you find the bosses in ruby to be impossible, try the following;
1.Open MW in two tabs on your browser.
2.Start the fight in the 1st tab. Attack henchmen until you are left with little health (and can't attack again without dying).
3.Go to 2nd tab, travel to New York and heal yourself.
4.Back to 1st tab and attack once more. You'll notice that when you click "attack" your health will be maxed and then fall again to where it was.
5.Keep doing 3&4 until henchmen are dead. Now you are left with the boss ;)
6.Ask for help from a LOW LEVEL FRIEND WITH AT LEAST 1 GRENADE. Don't leave the fight window!!!!
7.When your friend steps in to help you, the boss's health will immediately drop(!!!). Actually, the lower your friend's level, the more it will drop. Now, what your friend has to do, is throw at least 1 grenade to the boss and then attack until the boss kills him (a really heroic friend!).
8.After your friend has made his attack, go through steps 3&4 again. You will see now that the boss's health has dropped dramatically (poor boss).
9.Continue with steps 3&4, using all your consumables in between, until you kill the boss!
ps. when left with the boss alone, you have to be really careful not to leave the fight tab for too long, or he will regain his health. So what you have to do is attack him, then wait on the fight tab for 50-60 seconds and then QUICKLY go to 2nd tab, click "travel to NY"(although you already appear to be there), heal and then go back to 1st tab for another attack. Let me know if this worked for you too, or if you have any questions. ;)