Thanks, I was leaning towards keeping normal Marowak myself too. By covering all its weaknesses, I assume you mean Thunder and Fire punch? I've usually not really made a habit of teaching my Pokémon moves outside its typing that covers its weaknesses. I guess I'm too attached to STAB, and I usually just switch Pokémon of I encounter an enemy that's super effective. Is it really worth it covering all bases on the one Pokémon? I do have the TMs so I could teach them right now to my Marowak.
I'd rather teach Fire Punch to Marowak than Flamethrower to Gyarados though, since Gyarados has low Sp Attack.