The panzer is invariably completely useless. It's as ridiculous as a spearman that gets a bonus vs spearmen, or a catapult that gets a bonus when attacking catapults. And it comes so late. The panzer is the benchmark. Any worse UU has to be worse than the base unit it replaces.
The ballista elephant and the navy seal (mainly because it is late, and based on a peripheral unit) are almost completely useless.
There are a few possible candidates for being an actual downgrade: dog soldier, jaguar, numidian cavalry (all reduced strength), the samurai (needs iron), ballista elephant again (you might not want to target the mounted unit) and, really stretching it, the keshik (doesn't ignore first strikes innately). The only real candidates here are the dog soldier (can't axe rush), and the numidian cavalry (weaker against archers and horses).
For me, it's between the panzer, ballista elephant and numidian cav, but I think I've listed all the units that could conceivably be considered.
The ballista elephant and the navy seal (mainly because it is late, and based on a peripheral unit) are almost completely useless.
There are a few possible candidates for being an actual downgrade: dog soldier, jaguar, numidian cavalry (all reduced strength), the samurai (needs iron), ballista elephant again (you might not want to target the mounted unit) and, really stretching it, the keshik (doesn't ignore first strikes innately). The only real candidates here are the dog soldier (can't axe rush), and the numidian cavalry (weaker against archers and horses).
For me, it's between the panzer, ballista elephant and numidian cav, but I think I've listed all the units that could conceivably be considered.