Hero-change is style-adjustment lite
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Adjusting to needs on Antartic Peninsula
They lost game one and then one of their DPS requested they change their Winston to a Rein and they won the next two. The opponents were running Zarya and then Doomfist, and with their DPS countered the other team well. Possibly the Rein worked against their Brig well, and was a strong choice for holding point. Possibly the other team should have gone Ramattra to dislodge the Rein, since their DPS counter with Reaper was ineffective VS the Hanzo/Cassidy and Ana lineup.
ArX did a higher-than-usual healing orb usage, partly for self sustain. Maybe because it was CPT and the opponent was playing a Brig and Antarctic Peninsula is somewhat small for flanking, these all contributed to a more life-focus Moira.
Moira’s great flexibility means that rarely is it needed to change heroes to meet a situation; instead, change play style. But in this game, it does seem that it was the tank and DPS changes that made the win easier.