Perfect example for this is Aztec. Look at Skull Knights and Jaguar Knights. These units are constantly being brought up as useless units. Why is that? Simply look at their stats. Skull Knights have an atrocious 4.00 movement speed, which means they get kited by every single ranged unit in the game. If the Aztec opponent researched 10% infantry speed from Arsenal, Skull Knights will never attack any ranged unit again. They also have 0 ranged resist and only melee resist, which means they get destroyed by Skirmishers.
Now look at a similar unit, the Urumi. The Urumi has 4.50 speed, already better. But even more importantly, the Urumi has 30% ranged resist, which allows it to tank Skirmisher shots and defeat them in close combat. The Urumi is what the Skull Knight should have been. Its exactly the same role, but due to powercreep, the Indian civ, which got released later, has a great unit. Meanwhile, the Skull Knight is trash.
Another great example, very similar: The Jaguar Knight. They are also considered useless. They have 4.50 speed, but 0 ranged resist so they get destroyed just like Skull Knights by Skirmishers. Their melee resist is also only .10, which is low for a melee unit.
The usual army consists of Lots of Skirmishers or Skirmisher-Type units like Longbows/Yumi backed up by artillery. Both Skull Knights and Jaguar Knights have no reason to be used against this army. They are powerful anti-cavalry. But why would Aztec need anti-Cavalry? They already have Eagle Runner Knights and they have no artillery they need to protect. Their Skirmisher also only has 16 range (18 in Age III with temple card).
Another hilarious example: Compare Aztec and Inca.
- Inca get 2 War Huts from Age I to Age II. Aztec get only 1.
- Inca get endless 1200 wood shipment in Age IV, Aztec get only endless 1000 coin Shipment in Age IV.