There are plently of tournament results showing the contrary with people going undefeated against Drukhari or 4-1 playing against only Drukhari in tournaments. And this is against tournament players with minmaxed Drukhari lists, some of those counter lists I'm not even sure Drukhari could beat without extensive tailoring.
It's 100% possible to tailor against Drukhari, not all armies can do so successfully but many can.
Drukhari winrates at tournaments have already gone down a ton, it's still a bit high but it has gone down a lot now that counters are showing up.