i've been watching a lot of boss rush clear videos both on youtube and niconico and all of them either have at least a combination of gladio and either firion or lightning. what makes these three so good on the current JP meta? like what makes gladio stand out from other tanks? firion and lightning from other dps-ers?

i'm mostly curious about gladio considering he's the most 'outdated' among the three in the sense that both firion and lightning has their BT weapons, 80 crystals unlocked, and firion receiving a rework just recently and still from what i've seen from the boss rush videos i've watched literally all of them have gladio in the team, while some teams don't have firion or lightning, sometimes both