There's a big misunderstanding that open source, in and of itself, is more secure. Time and again this has been proven wrong (remember heartbleed?)
Where open source does benefit is a more timely and fair fix to a reported security bug. A company's closed source implementation may not be in as much of a hurry to fix security bugs if there isn't an immediate effect on the bottom line
Also, how's open source supposed to minimize fragmentation? Desktop Linux has a hundred flavors and even with a standardized ABI, there's no guarantees on a single binary working seamlessly across distros ( which is the reason for this like flatpack to exist)
Open source can introduce a kind of de-factor standardization when some project becomes the go-to solution for some domain, with almost everyone using it and contributing improvements. It is a type of network effect, the feedback loop being made possible by the open source development model. Examples include the Linux kernel, the GCC compiler[1] and even OpenSSL (which is what made heartbleed such a big deal).
Of course there still exists a long tail of alternatives, there is no stopping that in an open source world.
1. Arguably shifting to LLVM/clang these days. But note that clang for instance implements a huge amount of GCC compatible behavior (like commandline flags), instead of inventing their own.
Where open source does benefit is a more timely and fair fix to a reported security bug. A company's closed source implementation may not be in as much of a hurry to fix security bugs if there isn't an immediate effect on the bottom line
Also, how's open source supposed to minimize fragmentation? Desktop Linux has a hundred flavors and even with a standardized ABI, there's no guarantees on a single binary working seamlessly across distros ( which is the reason for this like flatpack to exist)