Sorry, my explanation was a little elliptical.
Our set-up period ended in T98, when we revolted back into Vassalage and Slavery. At that point we had 8 large cities, with varying degrees of development (Granaries in almost every city, Barracks in some, RHs in two, a Forge in one). There was no stack… maybe a Sword and a Xbow, at most.
The next fifty turns were devoted to conquest via siege units and support. These stacks are fairly self-sustaining, thanks to the high city attack strength of Trebs and the power of collateral. During the final ten-twelve turns, we switched to building Horse Archers, since these were the only units quick enough to reach the front line.
This allots ~50 turns to Treb production, and ~10 turns turns to Horse Archer rushing.
With 8 cities on T100, it is possible to whip 8 units every other turn. With ~28 active cities on T150, it is possible to whip 28 units every other turn.
However, on T100 other builds have to be considered. While you *could* whip 14 units from ~14 cities every other turn on T120, the reality is that Granaries, Barracks, Rathauses (etc.) are needed to sustain this.
In the last ten turns, the empire is now filled with ~28 cities (up from 8) that are out of revolt. By this time, there is no good reason to whip a Barracks or a Granary or a RH. Similarly, there is no good reason to hold back from cold whips, or whipping away (e.g.) a Spice or a Pig tile. It is simply more important to squeeze out every unit you can that could possibly reach the front line.
Our 1-movement stacks wiped the globe. HArchers only rushed two cities in total (one in Japan, one in Russia) and provided support in England.
tl dr?
(Xpost with bestsss.)