My point is sematics.
You can style your whole webpage with divs, but using main, nav, footer or whatever blocks is semantically more correct, because you group elements together that have a certain purpose.
A HTML Tag in the middle of a sentence is not wrong per se, but when parsing it a line break could signify two sentences where one has missing punctuation, instead of a complete sentence as your original intention was.
I don’t really care how the design you want is achieved to be honest, but I don’t get why the prof didn’t argue against.
While he advocates for it, that’s also a point that Martin brings up multiple times when he talks about his project “fitnesse”.
Basically saying that they left it open how stuff can be saved, but the need has never arisen to actually pivot to a different system.