It is different in this day and age, though, with respect to the time when the FOSS philosophy was born.
The difference is that now a lot of software is run as a service, which wasn't the case back than.
So, imagine MongoDB was used some 20 years ago (and it was GPL, as AGPL wouldn't make as much sense back then). A big company comes along, makes some modifications to the base product and tries to sell it. Guess what? They have to give the source code (including their additions) to whoever buys their version (including, potentially, Mongo inc.) so they would still be on a somewhat level playing field.
Enter software as a service. Since the GPL says nothing about software served via network, MongoDB goes under AGPL, which has provisions for this scenario. Amazon is not selling software copies, they're selling a service (hosting, integration, etc). So, even if they make additions to the source code and give them back upstream, they're on a completely different level from the small player (Mongo inc. or whoever else) and, since they're not differentiating on the code alone, win in the long run.
This all to say, it's not the promise/premise of FOSS that is flawed, it's just that the playing field changed.