And is there any kernal of truth to the myths of a Hero of Kavatch or Akatosh saving the city?
Finding out the truth about single heroes is usually very hard. While there are accounts of this hero of Kvatch, it seems strange that not even their species or gender is ever mentioned. It is most likely an invented figure to boost troop morale.
Sources:
The lusty Argonian Maid
Mysterium Xarxes'
Decoration Guide (Breezehome)