Well you won't, because you will get more than them. With 70% hit rate, there is a good chance of 100% in a 2 hit war, with 50% hit rate, there is very little.
It is a statistical fallacy that 50% hit rate on 1st attack means 100% with 2 attacks.
But that doesn't really matter. If you do both get 100%, I am quite sure that SC DO want a tie to be the end of a streak, even if it is a 100% tie. And yes, the game doesn't care in the least if you get your 100% with 45 attacks while your opponents take 70.
And nor should it. Only the final result matters. And the final result in both cases is that neither clan managed to defend a star on any of their bases. Why should they get a win for that?