I don't know anything about Mylar, but I would never trust anything but a jar. There are/have been at least 3 threads about what to trust and not trust for tobacco storage, and the OP has found fault with his bags. I don't get why out of laziness, I guess, anyone would not just jar bulk tobacco. Pipes are more expensive, but tobacco is not cheap. If you jar you:
1. surely protect the tobacco
2. Don't have to check the packaging for faults.
3. Don't have to worry about the packaging having faults
4. Don't have to post on a forum questions about the viability of bags
while if you jar:
you just have to jar
As regards the sterling question whether you just jar the tobacco or jar the bulk packaging with the tobacco inside it, I guess, the answer is that if you are asking the question you're a chowderhead! Are you going to smoke the packaging? Does having the tobacco inside questionable packaging going to improve the tobacco? C'mon!