The Mind Duel does the highest first. So if he has 2 or 3 Masters with 4-8 Slaves (Assuming they are all lowend Astral Users).

I know what the 'safety' range is, but you win with anything 4+ in levels I have found except with freak occurances (which can happen, but 1 in 20 or 30 MD's or so). So all you have to do is win against the ones who are higher and mop up the lower end ones. What would be even better is if it targeted the lowest first to MD to kill Communion Slaves, however this would still give Pythium an edge. Most of the time you'll be dealing with Light of the Northern Star, but other than that, the odds still work for the higher end Astral user.

For other players it may be less of an impact. If I'm playing an Astrally strong nation or pretender, I always script Mind Duel first on those mages who have 4+ Astral (After LotNS) And I rarely lose any while the opponent loses Grand Thamaturgs, Warlocks, Grand Masters, Nornas and others with much more than the % frequency.