They should not send just 1 unit and attack uselessly well-fortified cities.
Make them more clever: let them destroy roads and capture workers and
choose easier targets. Causing trouble is better than death for nothing.
Also they should wait to gather at least 2-3 units to make a raid.
Get back barbarian leaders we could catch and add an option to
release him for ransom or
execute to intimidate the bustards.
Barbarian unit weaker than regular is not fair. They should be at least
equal to regular in strength. Remember that some barbarian tribes were
very skilled worriors.
Add occational population boom. Barbarian hords should be able to sweep