Yes, of course. Think of all the stuff we wouldn't have without 3pps! Just off the top of my head, there'd be no Level Up, no Pathfinder, no Caverns of Thracia, no The Monsters Know, no OSE, no Rappan Athuk, no Zeitgeist, no Tal Dorei, no OARs, no Midgard, no Ptolus, no Strongholds & Followers, etc, etc, etc.... As a hobby, we'd be missing countless adventures, zines, campaign settings, player options, rules expansions, DM utilities, streams, minis collections, special edition boxes, and so forth. We probably wouldn't even have the nuTSR debacle to watch trainwreck-like.
D&D would be a soulless wasteland if we were stuck with one company's vision.