Reading this thread the necessity of a debug port depends largely on what kind of work you do (low level stuff without any I/O), whether you develop higher level software on the hardware itself or use a PC/simulator and last but not least programming style. Also when it comes to more advanced features (like profiling or 'realtime' debugging) it seems you still have to pay a lot of money for a good debugging environment. OTOH several low cost solutions are available nowadays which wheren't there in the 90's and earlier so setting breakpoints, stepping and watching variables is cheaper than ever nowadays.
I think it's more about "programming style" than anything else, and how you're used to working. I think older guys like me (and I'm not that old....42...but old enough) are simply used to working without a good debugger, and you get kind of good at looking at a piece of code and being able to imagine exactly what's going on, what timing issues may exist and things like that, because you just had to be.
It's kind of like doing arithmetic in your head. If the work you do requires that you do a lot of calculating, and I have had to do stuff like this from time to time, you just start getting a feel for the numbers involved, you learn tricks etc, and you end up being able to do a lot of stuff in your head much faster than whipping out a calculator. And then you don't do it for a while and it all goes away and you become stupid again.
A lot of my early career was stuff like radar processing and robotics. Often times you can't even get to the processor in question, never mind getting some sort of debug setup going, so it's not even really an option, but it's hard to imagine why you would ever not provide that sort of access during development, or at a minimum you should at least have a development board to work on so you can test your code, do you debugging if you have to and then try it on the real thing. This stuff is hard enough as it is so it's kind of dumb to limit your options, even if you don't use them 99% of the time.