Honestly, ever since they nerfed void, there are multiple ways to counter this. It was so much worse when the void bonus applied to the whole team. Glacial still can absolutely curb stomp assassin/void (those procs are so broken). Rangers pop them super fast as well (especially paired with glacial). Yordle/ sorc can do well also if built right. And while 3* don't make an auto win, 3* with a good comp does. Or if you had gotten your Kayle to 2 star, that makes a monster difference (she is broken AF). I just went against void/assassin and one Varus arrow with a 2* and seraph and deathcap killed half their assassins in the first shot. I also find a CC comp also does well as you can lock up a lot of assassins, but the you usually need 1 or 2 seraphs to get spells popping off fast.
Nobles will struggle because they just don't hit hard enough fast enough. In your case you might have done better if you had 3* as well or at least had Kayle more built (not that you can always control that) or if he was at 2s. Basically he landed a comp that was a complete counter to yours. It happens sometimes. It was like a time I landed an amazing Yordle team with a 3 veig machine gunning people with his ult, but then in the last rounds somone finished a full sorc combo and I lost half my team in the first second. Or I had a ranger team that was nuts, but someone had a CC team that shut down my back row long enough for their Gnar to get to me.
And I will still take a 4 ninja / 3 assassin / void team over void/assassin. Of course one time I had spatulas rain from the sky and made a 6 assassin/ 4 ninja / void (had to glitch on the last piece with the full bench) but it was nastier than nasty, but also a 1 in a million chance to get them all.
TLDR: you just got countered and had no way of countering his team.
'd I had FOUR
. My Pantheon had 
Jinx had Sword Breaker/Guinsoos.
