>writing a few thousand lines of assembly was what it took to launch a successful software company.

Yes, but that assembly was not DOS, and it wasn’t easy.

Microsoft purchased the DOS code, they didn’t write it. Of course, they did develop and modify DOS. But that was a clever (and lucky) business deal, not a technological accomplishment.

The real beginning of Microsoft was earlier, with Allen, Gates and Davidoff writing the Altair BASIC interpreter. That was a serious achievement.

They had never seen the computer they were writing that assembly code for. They did not even own any computers. It took them 8 weeks on a university computer they were not supposed to be using for that

“Altair agreed to meet them to possibly buy a BASIC interpreter… Gates and Allen had neither a BASIC interpreter nor even an Altair system on which to develop and test one. However, Allen had written an Intel 8008 emulator that ran on a PDP-10 time-sharing computer. Allen adapted this emulator based on the Altair programmer guide, and they developed and tested the interpreter on Harvard's PDP-10.

The finished interpreter, including its own I/O system and line editor, fit in only four kilobytes of memory, leaving plenty of room for the interpreted program. In preparation for the demo, they stored the finished interpreter on a punched tape that the Altair could read, and Paul Allen flew to Albuquerque to meet with Altair…

While on final approach into the Albuquerque airport, Allen realized that they had forgotten to write a bootloader to read the tape into memory. Writing in 8080 machine language, Allen finished the program before the plane landed. Only when they loaded the program onto an Altair and saw a prompt asking for the system's memory size did Gates and Allen know that their interpreter worked on the Altair hardware.”

https://en.wikipedia.org/wiki/Altair_BASIC

To be fair, i think you needed a cutthroat businessman leading the company. Which i guess is more or less the same today

And for such simple processors and systems no less! No descriptor tables to deal with, no memory management to configure. These days it takes a little processor inside the main processor, just to get things started. Those were golden times.

Replace Assembly with TypeScript/Rust/Go/whatever and as long as the idea is good and useful, same thing applies today.

More than a few people would rather die in poverty than put in the effort today even if you offered to time-machine them back with their finished product.