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.
Introducing a Captcha on a form on my website basically blocked bots 100% of the time. It’s arguably good enough from a practical standpoint.
If someone really wants to exploit my site, then they will find a way. You can only make it harder but never truly impossible if you don’t want to dispose of all convenience.