> "Mission Critical" - seven 9s reliability as being a minimum
I'd say that's pretty far from 'usually used'. Nearly nothing has seven 9s reliability. That's 30 seconds of downtime per decade - even applications which are literally life-or-death don't generally manage that, and the overwhelming majority of people using the phrase 'mission critical' would mean at least two orders of magnitude less reliable.
'Real-time', as you (sort of) say, has too many definitions to be especially meaningful without qualification. I've always been a little confused by 'soft real-time'. It generally seems to mean vaguely 'low-latency'; which is largely orthogonal to real-time. I guess it's really intended to mean 'general purpose' as opposed to 'batch mode'.
Either way it sounded like your earlier post said that a system can't be both 'real-time' and 'mission-critical', but then later you seemed to say that they can, which is confusing.