This is not true. In a 8 player multiplayer game, let’s assume there are 80 global items drops per some unit of time. In a personal loot scenario each player, would receive 10 items drop in the same period of time (10 personal drops X 8 players = 80 total drops). I both cases, 80 items drop total.
Your point only is relevant to leechers who do not understand the game well. “savvy” leechers will earn way more drops than good players because their eyes are really on stealing all the good items and do not need to concern themselves with dealing damage but just staying alive and swooping in. Therefore, personal loot actually discourages leeching and autopicker hacks/cheats.
Next, the trade economy is far more robust with personal loot. This can be determined mathematically as described here:
D2R: Personal Loot is a MUST for this game! - General Discussion - Diablo 3 Forums (blizzard.com)