Swampert can afford to take more out of its attack than many other similar pokemon mamoswine can only borderline run freeze dry because it takes so little out of its attack, and thats with Life Orb. In fact, it doesn't even take much out of it. swampert, has 20 higher base attack and 40 higher SpA. This means that it is capable of performing its job while not missing out on any EQ KOs that Mamoswine gets. In fact, its attack stat with that spread is almost 50 points higher than max jolly Mamo, and its lower base speed means that it can afford to run more efficient speed EVs than Mamoswine as it hasn't got a huge number of Pokemon that it is trying to tie with or outpace, i.e. the base 80 crew.
I called it offensive as it was SR+3 attacks, and it has all of its EVs invested offensively. Much like lead Garchomp does, in fact. Except they have different matchups vs the tier.