A bit rambling but felt like explaining a few design choices in my period game classes.
I try to keep my period games less power-gamey than pure D&D high fantasy, thus my preference for, and I loathe to use his term but it's Sunday and my brain is in chill mode, 'realistic' classes. Less powerful and fantastic. More grounded in 'reality.' The classic high fantasy versus low fantasy.
Thus traditional D&D Thieves, with their multitude of abilities are split into The Con-Man/Gambler and Burglar/Crook etc. More focused classes. Not a Fantasy James Bond or Batman do it all. On the flip side I also like my players to have characters who are more competent. That's the man reason I went to my formula of 10 + level (or half level) + ability score modifier for most class abilities/'skills'. Percentiles can still be used as in traditional games but my players found the d20 mechanic smoother for their needs, I like it as well. Sometimes nostalgia hits and I'll refer to percentiles or use the generic 'as a Thief of equal level' to make some of the write ups more accessible to traditional DM's. Such was the case with my Revised and New Fantasy Classes.
The period games classes for Victorians, Westerns, Colonial, Pirates, and even Modern are designed to be used with each setting as needed. That's why most of the classes in different settings (such as the Gambler and Con-Man) are the same, just renamed for flavor, variations on a theme.
The real change is in the setting. Again, I like more competent characters and want my players to enjoy being pretty decent at things when beginning a character, thus for combat I changed the hit bonus to a Combat/Non-Combat class orientation and they still have a better chance to hit than in most traditional D&D games (+1 per level for Combat/+1 per 2 levels for Non-Combat). The Western Setting has everyone using the +1 to hit per level. Thus porting over a Physician requires that slight adjustment but it is fitting for that setting to have the Physician PC be able to fight better. It's a genre convention. Classic Victorian and Colonial Physician characters are non-combat roles.