Possie Hips aren't that bad.....Compared to RC:
Cost/Per/Pop: Hip=36 RC=45
HP/Per/Pop : Hip=50 RC=52.5
Att/Per/Pop : Hip=3.3 RC=4
RC also have better armor.
Possie Hipps are slightly less pop-effective than RC, but signifigantly more cost effective. Don't forget stables are also dirt cheap. Researching the Myth Upgrades availible makes them better than RC all around.
Now, build time. For the sake of arguement, lets say both players have 6 rax in classical devoted to producing 90 Pop worth of Calvary.
Possie: 18 Pop every 20 seconds, 100 seconds to produce 90 Pop.
Norse: 12 Pop every 18 seconds. 144 seconds to produce 90 Pop.
Now Heroic. For whatever reason, both players still have only 6 rax devoted to Calvary. I can do more if you want, but it doesn't matter much.
Possie: 18 Pop every 15 seconds. 75 seconds to produce 90 Pop.
Norse: 12 Pop every 18 seconds. 144 seconds to produce 90 Pop.
Possie's Calvary isn't just above average. It also has a large advantage in Cost/Time effectiveness, which can be crucial.