From what we understand, Team Power won’t take into account event buffs, as it doesn’t use any of the four main stats as factors. Factors of Team Power: Rarity (actual, not base), Level, Traits, Hero Mastery, Guild Masteries, Guild statue bonuses (the temporary ones), Stat bonuses for level 10 kingdoms, and likely the double and triple bonus counterparts.
More related to the topic: I believe an event around defense teams would be nice, as it would hopefully get people changing their defense teams more and providing more variety. But at the same time it would result is a lower win/loss ratio for all but the top players, as it would probably require you to use troops you don’t have leveled/traited. Also losing isn’t ALL bad, since it gives you revenge chances, which give you bonuses after certain numbers of revenges.