Erasure coding is an interesting topic for me. I've run some calculations on the theoretical longevity of digital storage. If you assume that today's technology is close to what we'll be using for a long time, then cross-device erasure coding wins, statistically. However, if you factor in the current exponential rate of technological development, simply making lots of copies and hoping for price reductions over the next few years turns out to be a winning strategy, as long as you don't have vendor lock-in. In other words, I think you're making great choices.
I question that math. Erasure coding needs less than half as much space as replication, and imposes pretty small costs itself. Maybe we can say the difference is irrelevant if storage prices will drop 4x over the next five years? But looking at pricing trends right now... that's not likely. Hard drives and SSDs are about the same price they were 5 years ago. The 5 years before that SSDs were seeing good advancements, but hard drive prices only advanced 2x.