I took a look at the two big Extended tournaments since the points update ( Dathomir and Corellia ), which were both won by Nantex swarms. Defining "Nantex swarm" as a list with six Nantex, there were nine of those lists across the two tournaments and every one of them did very well.
The combined record of those nine lists was 46-8 in Swiss, or 41-3 if you exclude the mirror matches. In the elimination rounds their combined record was 19-6, or 17-4 excluding mirror matches.
That leaves a grand total of seven non-mirror-match losses, and the lists that won games against them were:
- Vader (FCS, Afterburners) + Soontir (Crack Shot + Targeting + Shield) + Grand Inquisitor
- Redline (ProTorps + Prox Mines) + Whisper (Passive + Fifth Bro) + Grand Inquisitor
- (2x win) Seventh Sister + Fifth Brother (Passive + Homing) + 2x Sigma (2x Crack Shot)
- (2x win) 6x Trade Fed Drone (3x Discord) + 2x TUB (2x Plasma Torps)
- Grievous (Title) + 4x Nantex (4x Gravitic Deflection, 3x Crack Shot, 1x Marksmanship)
So... mostly my conclusion is they don't lose to much at all. Those win records are pretty insane. Of their few losses, a little over half were to ace-y lists that could move after the I4 Nantex either by initiative or bid. But it's not much of a pattern, and they certainly beat more of those types of lists than they lost to.
Hopefully we'll see someone figure out a counter by the next big tournament.