I think we should use the number of attacks used to hit Perfect in the event of a double perfect wars, ie how many attacks each clan used to achieve the perfect.
EDIT: I think a better way might be use the number of defences (2star and below) by the top 5 TH of each clan as tiebreaker
It should not end it draws and should allow a clan with a 70% hit rate to be declared a winner vs the opponent with a 51% hit rate.
I mean even non-perfect wars that end in ties in stars (which mean both clans have very similar hit rates) are broken using average destruction.
A perfect war tie is so broken as there is no meaning above a 50% hit rate which is very possible in current TH13 meta.
If SC does not want to change the hit rate by balancing, they should at least add in a tiebreaker so that elite clans with higher than 50% hit rate can still compete fairly.