Just occurred to me...

There are civs that have cavaliers but not paladins.
There are civs that have two handed swordsman but not champion.
There are civs that have xbows but not arbalests.
There are civs that have pikes but not halberdiers.
There are civs that have CA but not HCA.
There is a civ that has skirms but not elite skirms.
There are civs that have capped rams but not siege rams.
There are civs that have light cavalry but not hussars.
There are civs that have onagers but not siege onagers.
There are civs that have scorpions but not heavy scorpions.

But there are no civs that have camels but not Heavy Camels.

I guess same applies to battle ele and eagle.