Interesting article. It would be more interesting still to compare design guidelines with languages like German that use roman letter capitals differently in general.
If you look at British writing from even 200 years ago, title case was used all over the place. In fact, capitalizing the first letter of a word was just generally sprinkled around to add emphasis. Only much later did the conventions around sentence casing and title casing come in.
Ultimately, the effect of capitals changes as people get used to them. Early computers didn’t have space to store two sets of letters (upper and lower case) and so you just got block caps and lived with it.
Personally I think the monks had it right. Large illuminated letters at the start of each paragraph please!