Supplementing Ground Slam

Something I was curious about: Is it necessary to supplement an AoE ability like Ground Slam with something more single target (like say Glacial Hammer) when fighting just one enemy?

Since Ground Slam only deals 80% of your base damage while something like Lightning Strike or Glacial Hammer deals 130%, it seems like the latter would be a good choice to bring along for those times you've killed all the mooks and just have a single rare/unique/boss to deal with.

However, considering how many support gems come into use later in the game I was wondering if a single aoe skill supported by 3-5 gems would be better than a single target gem with only 2-3 support gems.

4-link heavy strike will outdps 5-link ground slam but not by much. If you don't have enough gem slots you can get pretty far with ground slam only. What I'm doing currently is using 5-link gs+melee dmg+multistrike+fa+crit multi and I carry heavy strike gem in other slot. With harder bosses I just do a little gem swap and see them melt.