There's only 1 fighting sequence that has a 'bug" in it : If you have a warrior at full health, you'll NEVER lose to a barbarian.
if you have one damage or so on that warior, you may lose, but never at full health.
Now if you use an archer (same attack ; 1), you may lose the attack!
I don't understand why, but it sure is strange...
Mathematically the pikeman can beat the tank in the game but it looks so stupid and funny though
I remember when I was trying to protect my Endor moon base -- I had stormtroopers, AT-STs, some TIEs -- and these little savage teddy bears armed with sharp sticks and rocks attacked en masse and actually took my compound! CRAZY!
I think you have to use your imagination when playing Civ games. You could imagine that, within those odds of a pikeman defeating a tank, it also includes the odds of them getting their hands on a weapon or other means of doing the job. Maybe those pikemen got their hands on firearms and took a few lucky shots, or maybe they planted explosives that took out the tank's cannon, then just opened the hatch and skewered them.