The original design, years in the making, was based on batteries that would never catch fire.

They have moved from never catch fire, in a period of a few months, to batteries they hope will not catch fire, with features to enable survivability should a battery catch fire.

If this new design is appropriate, that earlier design was engineering malpractice.

I doubt this design would be the outcome of the same Boeing design engineering effort without the get it to market time constraint. Just like when a web service goes down mysteriously and the engineers desire is to take it down and debug it and the required response is to patch it, and get her flying again. But I wouldn't term that "design" or "engineered".