Indeed, I’d have no problem using Smalltalk for just about everything, including writing an operating system!
I submit that Smalltalk is great for software engineering at scale. You don’t need static typing. You don’t need the numerous fancy features that bloat languages such as C++, Scala, Swift, and Kotlin.
But Smalltalk is not ideal for all applications. For example, I wouldn’t use Smalltalk for developing high-performance AAA console video games for PlayStation and Xbox. I wouldn’t use Smalltalk for critical, realtime control systems in nuclear reactors and flight avionics. I wouldn’t use Smalltalk for creating shrinkwrapped, retail software like Photoshop and Final Cut Pro.
But web, desktop, mobile, data science, machine learning, IoT, virtual reality, robotics, etc.? Absolutely. Smalltalk would be great in these areas.