Yes, yes it would. They meant to say that it would improve performance (if done well, which it was). That improved performance would allow it to run on a wide variety of devices, including those with low specs.

Also at the time writing for x86 only would have been plenty portable. Even today that would cover "standard" PC architecture. (Although nowadays you probably want to put it on mobile devices, gaming consoles or macOS, so not ideal.)

That idea comes from the tycoon games because they run on newer windows versions easily. But it's not because they were made in assembly. Any programming language can do that as long as the program doesn't depend on specific OS features that get changed or removed. I think assembly is just synonymous with everything being from scratch.

I kept scrolling for this comment. Writing in assembly means you can only write for one specific instruction set. The innovation of programming languages was not just making things easier to write, it was the compiling step which could take the same code and produce machine code output for different systems, making it much easier to support multiple platforms.