He is right. 1 strong attack is way better than a few weaker ones, even if damage result is the same. When fire main does 1 attack and lightning does 4, you save few seconds, so your overall dps (damage per second) is higher. Because fights last 4 rounds and you do those multiple times, sometimes such small differences can add up to whole additional fight. This is also the reason wind main shouldnt use clones passive- even though they deal good dmg, they slow down overall dps.

Regarding your main team: LM gets buffed, yes. But konoha lineups have better synergy and those buffing token ninjas like iruka, asuma, barrier one also deal some dmg. 9tails is a dps check, every single point of damage you can do in the shortest time possible matters.