I'm not at a real computer to check, but I think $400m barely paid back the investors.
And speaking as a former NeRD (NeXT Registered Developer), it was definitely a flop. The computers sold only in a few niches, and they had to kill off the hardware entirely. The OS and the dev tools lasted longer, but they wouldn't have survived more than another few years.
Yes, NeXT and NextStep were flops as products: nobody bought them. Some of the OS technology was great, and it eventually got incorporated into a successful product after a lot more work. But a flop with good tech is still a flop.
And speaking as a former NeRD (NeXT Registered Developer), it was definitely a flop. The computers sold only in a few niches, and they had to kill off the hardware entirely. The OS and the dev tools lasted longer, but they wouldn't have survived more than another few years.