User blog comment:12th Supernova/Chapter 786: 10 Minutes/@comment-5398287-20150514115305/@comment-5398287-20150515102814

Even then, though, an "inexperienced" Logia-using giant could be a legitimate threat. When Sabo first used Hiken, the flame his shot was the size of his fist. Now imagine if it was the size of a GIANT'S fist.

And if Logia doesn't matter, then what about a versatile Paramecia like the Gomu Gomu? Gear Third inflates Luffy's normal-sized body parts to sizes matching those of a giant, so imagine what kind of power a giant could gain from inflating THEIR fist by an equivalent amount.