Grohk using maelstrom can farm easy damage off of your team using Luna. Your best bet is to hide Luna behind a shield if you're capping the point with Luna. With totemic ward, he counters Luna's rush and your ult.
If Grohk is using totemic ward, he does have cc immunity against your ult and rewinds, but you can just 2 tap his base totem without buying bulldozer. If Grohk is using maelstrom, your stasis field eats his shock pulse, preventing the spam.
When Khan tries to grab you, rewind him. When Khan ults you off the stage, use setback. You can even rewind him after he battle shouts to take away the heal. And with that, you've taken away Khan's best abilities.