SunOS evolved to be a great file server and "network computing" server, whereas HP-UX evolved to be a better multi-workload commercial server. Horses for course

SunOS evolved to be a great file server and "network computing" server, whereas HP-UX evolved to be a better multi-workload commercial server. Horses for courses—and they often ran on different turf. You're also right to shout out out some of the other innovators: Data General's DG/UX did a great "let's redesign the kernel for multiprocessing and NUMA." IBM's AIX had kernel threads, pageability, and preemptibility at a time when no one else did (plus JFS, LVM, and eventually LPAR isolation). And Sequent DYNIX/ptx had some impressive multiprocessing (RCU) and large DBMS optimizations very early on. HP was by no means alone trying to engineer away Unix' early weaknesses.