Obviously I'm in favor of getting a second big; you are just missing the point
It's not like we can be like "ooh I want Gortat, now he's here". Many teams would love him, which raises his value.
While its not worth it, Phoenix is looking for a Sullinger+Lee for Gortat type deal. Even if you ignore the loss of Sully's production this year, because Gortat can put up similar numbers, the loss of the SG depth is huge. We trade Court, who is our backup SG? You speak of someone like KG fouling out, what if Bradley fouls out or gets injured? You want Terry and Barbosa to be our SGs, to guard Dwyane Wade?! Lebron is plying more of a perimeter style offense this year anyways, so it's not the same to how KG guarded him last year.
I would love an upgrade at C, but not to compromise our guard depth in return