The 4.87" x 2.31" x 0.30" envelope arose with the 5, a year before the 5S.
True, but there are some design differences (including the addition of TouchID), while the 5S and SE are almost identical. (You also mentioned the 5C, which was an alternative to the 5S.)
Sure. I mention the 5C because it was the real budget device. On the day it was released it had internals the same as the previous year's 5, instead of those of the 5S released on the same day as the 5C. The SE, by contrast, had the same guts as the 6s. People seem confused about this.