A DRG uses Geirskogul, attack them ASAP, force them to lose their momentum to use Guard or end Blood of the Dragon early.

A DRK charges at you, bind them with Gravity or silence with Bard.

You can even neutralize BH5 DRGs and DRKs by just using MNK LB when they're charging in.

Finally, see Salted Earth, just RP walk away, it's that easy to dodge. If you get stuck, use Guard. Or don't even get sucked in, DRKs are always so obvious when they just run in. And DRG's LB is ridiculously easy to dodge.

The really problematic class is actually Astrologian, sorry to say but I don't think you're very skillful if you think DRK and DRG are problematic ^^