BeOS offered the same FIFO scheduling mechanic that allows Linux to support soft real-time.
RTLinux was a hard real-time OS which runs Linux as a lower priority service you can pre-empt with your actual hard real-time stuff. Similar systems still exist today. They work fine, if, in fact, what you needed actually was "hard real-time".
If your idea of the potential consequences when your system misses a deadline is more like "Some users are annoyed and demand refunds" rather than "I might go to jail for manslaughter" or "The $40M space probe turns into space garbage" then "hard real-time" probably wasn't what you needed after all.
Is Haiku only soft real time? Yes, and I never said anything different.
Does it do a markedly better job at making real time commitments than NT or even RT-Linux? Absolutely mainly due to how much simpler of a kernel it is.
Also, I'm going to throw out there that if you're going to get uppity about hard real time guarantees out of nowhere and throwing out concepts lime manslaughtee charges out of nowhere, I hope that you're only choosing sel4 as last time I checked it was the only kernel that backed up it's guarantees in a way that it can be checked.