Well, not memcached, load-balanced, Kubernetes'd production applications, but computers were certainly running large, multiuser, had to be up with five or more nines of uptime back then. But you're right -- early Unix wasn't running those. Those were handled by IBM iron and, later, VAXen running VMS. Real operating systems. And then college kids who had read the Lions Book as undergrads and thought an operating system was shaped like Unix entered the workforce and decided that VMS and System/370 were too stodgy, and put Unix on those same VAXen. But the operating model of Unix was not designed for real applications with large, concurrent workloads, and the UI was not designed for the people on actual worksites, even in its heyday. (VMS, famously, was designed to be correctly usable assuming the operator is tired and hasn't had their coffee. Unix shells were designed assuming 100% perfect memory and an allergy to actually typing.)

I'm sure DonHopkins will be along, endlessly quoting his own contributions to the UNIX-HATERS Handbook, to elucidate.