Castle blood is an example of the poor pop system in AoC. Look at it, it's pitiful, inf. resources and then the biggest unit generally wins. Which should weigh more in a pop system and elepant or a militia? While cost is important, resources are infinate, but there is no quantity barrier except for, 200 of any unit.
I can't dream of why someone would want it this traditional way, I think that it should be balenced. The reason that elephantes cost more, is just to get you to use less of them.
To be honest, the cost system would work perfectly, if the units were finely balenced. but there are units that are never used. they are that way for a reason, and a decent pop/cost system could fix that, instead both AoC and AoM have flawed systems.
If I havent already said so, AoM's system IS better because it is a rush game, as they all are, that encourages booming with the housing system. AoM also has many other details that make it unfair to that, no, not that unit, it costs to much, or, it's too unpop effective. The same goes for AoK/AoC, but to a far lesser degree.