This was pretty much the high point of "coder machismo", along with Eric Raymond and his power tool analogies. Presumably this is also why the kernel doesn't have a test suite. Interesting to compare with the other paragon of software development processes, SQLite, with its vast test suite. It doesn't have a "debugger" per se, but it does have some tips: https://www.sqlite.org/debugging.html

Always difficult to tell what the cost of this was. What features did we not get because developers were put off? What problems did it prevent? How did this affect downstream Linux ecosystem development and culture?

Re: use of debuggers, I've found them most useful when dealing with other people's code; you can short-circuit a huge amount of "where is the code that does this" or "how did I get here" by just setting a breakpoint and getting a stacktrace.