The sealed bags aren't worth spit. Given time the contents will turn to dust. Jar or seal in metallized mylar for long term protection.
I don’t jar anything. Most of my stuff lives in tins and bags. I have an insane amount of stuff open at any time. Takes me a few years to get through it with all the rotating. But I live in a very mild climate, so nothing seems to get too dry, or wet.
If it makes you feel any better, I have a gazillion 8oz mason jars in my rotation. I obviously prefer to jar my tobacco but if you're happy with your bag and tins, you should continue what you're doing.
It's Mylar that's been coated with metal. Mylar on its own is not impermeable, so contents will dry out. The metal coating drops the permeability to near zero, and if you buy the 7mil food grade bags, it is zero. For long storage, heat seal the bags. You're good for years.
A lot of tobaccos are packed in Mylar, like all of the Esoterica bags. GL Pease was bagged in Mylar in the early 2000's and it's held up really well. So no, no concerns.
I mylar all my square tins (SG mostly but some Mac Baren also). They tend to be hit and miss on getting/holding a good seal. I don't seal any circular tins. I cellar C&D and Peterson style tins as they come and they've all held up nicely. They do need checking occasionally to ensure seals are goood
