There are a number of Varelsi that are around the area and want to see that you do not succeed with the Harvester come to collect the Shard. The first round has Marksmen, Skulks, Berserkers and Primal Thralls with Primal Thrall Bombers on the occasion.
When you make it to the second part of the wave, you will be dealing more Thralls than Varelsi. The Thralls will be coming in through the various doorways on the lower level and the balcony above. If you need to get to the upper level, use any of the jump pads in the area to quickly get launched upwards. This means more of the Primal Thralls encountered earlier but also Thrall Gunners and Evolved Thralls.
The third part of this fight brings back the Varelsi. More Marksmen and all the others to contend with. So Evolved Thralls and the other variants as well will continue to come after the Battleborn. Use the Radar to quickly locate them and kill them.