The things that seems to make the game longer is town defence.
As soon as someone has a wall technology, adding 10 defence that come back every turn, you cannot exploit the Catapults to inflict massive damages in the early game that easily or just focus on putting a lot of unit to have an edge and doing a lot of small damages.
Also, those damages in early game stay and never recover. So if you deploy one or two Catapults at the start, you can crippled the enemy with 15 to 25 damage that will matter a lot in later stages as Health never goes up.