This leads to runaway STEEM inflation whenever SBD falls under $1 (currently, $0.62) as extra STEEM is printed to compensate for it

That is not what happens at all. There is never any extra STEEM printed to make up for SBD being undervalued, whether it is operating in the haircut/recovery zone (as it is now) or not (the rest of the time).

As I suspected from reading the original post you have some misconceptions about how the mechanism actually works.

Anyway, it isn't really worth getting into IMO because SBD is really the least of the problems. If STEEM otherwise had some reason to go up in value, SBD wouldn't get in the way (in fact it would help), but unfortunately it does not.