I agree with your assessment regarding NeXT. NeXT can be thought of as a pragmatic Smalltalk machine that was adapted to the needs of the higher-education market that NeXT originally courted up to the release of the NeXT cube. For example, instead of pure Smalltalk with its live object environment, NeXT chose Mach + 4.2BSD as its foundation (which made NeXT able to run Unix software), and it chose Objective-C as the primary programming language for implementing NeXT software, which added Smalltalk's object system to C.

I've been knowledgeable of NeXT's history for over 15 years (I was a high school student when I first learned of the history of NeXT), but I'm curious about the decisions that led to NeXT picking Mach as opposed to pure 4.2BSD? I'm aware that Avie Tevanian, who was a PhD student at Carnegie Mellon who worked on Mach, was an early NeXT hire, and I'm also aware that before Steve Jobs founded NeXT, he led a project called the BigMac which would have integrated the Macintosh with Unix (https://lowendmac.com/2013/apples-bigmac-project-failed-prec...). NeXTSTEP could be thought of as a continuation of the BigMac project.