With non-unique units paladins can only be countered by upgraded halberdier, heavy camels or a huge mass of arbalesters. Monks counter them in small numbers but in late game when they're massed they're almost unstoppable unless you have halb/camel in equal numbers.
Well even arbalesters get slaughtered by Paladins, unless we are able to push them behind a wall or a corner with only a very tiny attack area for the Paladins.
I think even in open ground if you have a big enough group you can still trade well. Ethiopian arbs fire 25% faster. If you micro the arbs to focus on individual paladinsthey can one shot paladins and their attack surface area increases with the sqrt() of their numbers. For sure it's a lot more work than spamming halb.
The Vikings are an incredible civilization. Berserks are one of my most favorite units. Not sure where they are today, but they totally matched Paladins in terms of attack strength back in the day.
For real, though, it's really great to see this game continue to live on.