This is a strange argument from silence. Jacob ended up being richer than both Abraham and Issac. Just because Genesis did not record him regularly tithing, its plain silly to say Jacob did not do it.
Imagine if the Bible included Jacob, or Issac or Abraham tithing, it will sound like this
Genesis 18:33 When the Lord had finished speaking with Abraham, he left, and Abraham returned home, and Abraham tithe to the Lord
Genesis 26:12 Isaac planted crops in that land and the same year reaped a hundredfold, because the Lord blessed him, and Issac tithe to the Lord.
Can you see how silly it is for the Bible to record down every time these people tithe, in order to convince us Christians 2000 years later that tithing was before the Law?