formidable legendary can also help you survive viktor's ult

Viktor's Barrage actually spawns explosions on the ground instead of dropping them from above. Moving backwards while he is locked on to you will make them hit your shield if you get the center of the blast off you and in front of your shield.

You can throw your frag grenade over or around Fernando's shield to damage enemies behind him.

Buy the Life steal and Demolition items, and deal the most damage you can to him, shooting or throwing grenades.