I think it safe to say that during the Edwardian Era (roughly 1900-1919) gentlemen's Highland attire became fairly standardized. The cut of day wear jackets tended, then as now, to follow general trends in men's fashions, slowly evolving into the "standardized" jackets that we see today, hardly changed from the styles of, say, 1939.

Evening wear followed in much the same path and, again aside from minor differences in the actual cut, today's formal doublets and coatees would not be out of place at a dinner or ball in 1925. Because there were far more formal dances, etc. before 1960 more people tended to own their own (usually off the peg) formal attire. But for those who didn't-- or couldn't afford to-- "own their own" there were numerous firms that could supply rental jackets, and even kilts, back in the 40s, 30s, 20, and beyond.

I think the reason so much of what we see to day looks "cookie cutter" is down to two factors:
1) Because so much of it is poorly made, compared to the hire garments of 30-40 years ago;
2) Because there are far few occasions to wear formal attire there are far fewer "accessories" for gentlemen.

With everyone wearing a made-in-China Prince Charlie, a bovine sporran with chrome plated pot metal cantle, and white, throw away, socks a certain "cookie cutter look" is, sadly inevitable.