I think the die cutters modified the Capital letterforms to suit their purpose and, with their inate sense of beauty and style, produced an alphabet whose letterforms were much more uniform in construction and proportion. Most modern typeface Capital alphabets employ this style of proportional letterform construction. I think that designers of modern typefaces have been enormously influenced by the letterform constructs found on Roman coins -- albeit maybe unconsciously.
I am not aware of exactly what kinds of burins (engraver's chisels) the Roman coin die engravers used. I think they probably were undergoing constant design modification throughout this period of history. Some die engravers probably used burins of their own personal design thereby producing somewhat atypical letterforms. One thing for sure, not all die cutters were born with, or developed, equal skills (calligraphers and stonecutters also) -- particularly with regard to letterform rendering. To my eye, there was a group, or school, of die engravers during the reigns of Tiberius, Gaius (Caligula), Claudius and Nero who produced especially exquisite coin inscriptions.
Rendition of letterforms of Julio-Claudian coin engravers
In any event, the Roman Imperial coin engravers produced letterforms of uniform excellence using (by modern standards) relatively primitive metal cutting tools.
Exemplar of Capitalis Monumentalis Inscriptional letterforms -- obverse of Claudius As
Note relating to late Empire vs. early Empire coin Inscriptional letterforms
Constantius Chlorus Follis - Late Empire ..... Claudius As - Early Empire
Galerius Follis - Late Empire ..... Tiberius As - Early Empire