Systems such as Linux, MacOS and windows? All terribly broken and unusable. Seriously you need better sources or more experience. POSIX is alive and doing better than ever.
Now we're splitting hairs, Linux is POSIX compliant, but not certified as certification costs money. Windows is also compliant through Linux subsystem. On Linux side there are also distributions which are POSIX certified which then makes Linux certified as well. It's just the windows, which also was certified at one point, early 1990s and air force. So that makes me right?
Not exacly posix isn't 100 times slower and 100 more expensive that other is more inconvenient standard, becouse is simply old standard, bitcoing is a product in itself not a protocol,and this product don't fulfill the need for fiat currency becouse is expensive to transact, and slow te best you can say is that is difficult to make changes but bitcoin isn't exactly the one of 10 years ago, protocol change to acomodate for more transactions and most votes are concentrated in few minority of big stakeholder, making kmposiblw to reduce comitions or change significantlythe protocol.