As to C, the math is simple. If each tenured professor has tenure for 30 years and has a single phD student graduate every 5 years, statistically the number of tenured professors need to grow by 500% in 30 years (over 6% per year) for all those phD students to get a tenured job.

Now, there are hot topics that may see something around this amount of growth for a while, but many don’t. For example, in biology, genetics and biochemistry may somewhat have that growth rate, but if you’re in any other subfield such as ethology, forget it. If you’re a historian, did research on some ‘obscure’ language such as Middle English, or are working in some corner of mathematics that doesn’t have direct applications, you can forget it, too. If anything, the number of tenureships in those fields is shrinking.

Of course, many tenured professors have a lot more graduating students during their career. In medicine, one a year isn’t uncommon. That would require a field that grows by over 12% each year.

The deceptive thing about this is that, as a phD student, you don’t see those 30 competitors. You’ll only see maybe eight to ten. Some of them graduated a few years before you, others will start after you graduated.