I feel completely useless as a caster support with the new duskblade/lethality stuff. Do I just move on to Tank Supports until this patch is over?

I mostly play Nami, Sona, and Karma as my main supporting champions with the occasional Taric if I see that their whole team is AD based, and for the most part I've done pretty well with them this season. Ever since this patch though, I feel like I've been losing a lot more. If the game doesn't end in 20 minutes where my team is stomping the other one, their Duskblade Khazix, Wukong, Talon, or w/e champ that works with that busted item jsut one shots my ADC or Mid Laner, and I barely have the time to react to that. So I'm at a lost at what to do. Do I build Solari right away? Get Knight's Vow?