I'm not a string player (I once tried to learn viola da gamba but gave it up), however I've known a lot of early music string players.
I was once told by a professional Baroque violist that in order to perform all the styles of music from the earliest days of the violin, viola and cello to the present day, if one wants to observe historical performance practice, it is necessary for a string player to own six different kinds of bow, each one constructed differently, and particular to a particular historical and national style period.
So the differences are certainly not cosmetic. Furthermore the music written in each style period (with regard to phrasing, etc.) reflects the capabilities of the design of the bows in use when the composer wrote the music.
Most importantly, up until about the year 1900, all string instruments had strings of sheep gut rather than the modern steel strings. Sheep gut strings have much less tension and tensile strength. I believe that bows from the historical period of sheep gut would have a different design and lower tension in the bow hairs because bowing sheep gut strings would be quite different from bowing modern steel strings. If the modern bow is designed for bowing an instrument with modern steel strings, it stands to reason that it would be designed and held and played differently than a historical bow designed for bowing sheep gut strings.