His thesis is only slightly longer than typical PhD theses, I think.

I would say 300 is more than slightly longer. Varies by institution and style, but 100k words, 4-5 collated papers, 100-150 pages maximum are quite common.

I would be concerned as an examiner if this came across my desk, more so if I read the colophon where the author comments that they intended to write their own typesetting system, before reading Knuth and wisely concluding that they were unlikely to do anything better than TeX. Top tier yak shaving there.

Yes, but the other things in the OP list aren't theses, they're journal papers.