Doesn't matter whether a team is predictable or not. Your argument about creative movesets applies to every single team with the advent of team preview period
I can't comprehend what you mean by lack of utility. I guess we don't have any... phazing? What are you getting at?
As for coverage, boosted dragon moves have perfect coverage for all intents and purposes as far as anyone should be concerned. Also gliscor's eq isnt a 100% certain ko on terrakion. Gliscor is weak as shit.
Playing aggressively is always advantageous, the pressure will be on your opponent which will lead to mistakes. As for sacrificing, it is an integral part of every style of play and is unavoidable.
A better reason to dislike heavy offense is:
1. its easy to mess up because there is no opportunity to scout movesets (though team preview helps heavy offense make better guesses)
2. Once you mess up it may be hard to regain momentum, and the complete loss of a sweeper is often too much of a disadvantage to overcome
3. Using moves like outrage can lead to you getting counter swept, but there is no alternative
4. Great reliance on speed, so anytime you are slower or can't move first youre screwed
5. giant weaknesses to gimmicks like trickroom and tailwind, even focus sash pokemon or sturdy pokemon.
Also any offense that isnt hazards+5 set-up sweepers can just be said to be an offensive team. hazards+ 5 sweepers is called heavy offense, stathakis is generally credited for naming the style that originated with him.
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