I think it's a little off to try to compare the osprey in airplane mode to other airplanes and the osprey in helo mode to other helos. It doesn't make sense. It's not boasted to be faster than regular airplanes, nor better at lifting than normal helocopters. The V-22 can't "fall short" of either of those regulations as it doesn't fit into either. Those limits are designed specifically for aircrafts of those exact builds and functions...not a tilt-roter.
The fact is the osprey combines functions in away that grants a tactical advantage. If we sent in a plane, sure it can get there fast, but it can't just stop and load people on and then get out quickly. We could send a helicopter and sure it can do a quick insert/pick-up and then leave...but i won't get there fast or leave fast. The osprey gives the best "hit and run" option. Get there fast, pick 'em up, and leave fast. It may not pick up as well as a helicopter and it may not fly as fast as an airplane, but it does enough of each to make it effecient and a game changer.
Also, you guys vastly underestimate this machine's ability to defend itself. It is allowed to make defensive/evasive maneuvers. Those are not "aerial combat maneuvers." Belly mounted gun and and ramp mounted guns are installed (Now, I am talking USAF, I couldn't tell you for USMC). Also, I don't know how much of this information is sensitive, so I won't name specific equipment, but the USAF version has several anti-missle countermeasure systems installed as well. Those features combined with it's fast escape speeds make it a formidiable option.