@Fire Fist:
As for land zoans, do they really help the user? Was Lucci really that much stronger with his fruit? It's not like his moves are going to change because of his fruit. And Kaku could already use all four limbs as a weapon, he didn't need to go into Giraffe form for that. I'm sure he could've cut the building in half without his Giraffe form. And as for pasta machine, that was just too weird to comment on.
Yes, there probably was a huge increase in strength for the Zoans, specifically the carnivorous ones, though Kaku's enormus animal probably negated any sort of bonus carnivorous zoans had over him. It's probable that, although Jabura and Kaku were simmilar in douriki prior to using their forms, Kaku was a h_uuu_ge amont stronger than Jabura, even if Jabura was better able to make use of Rokushiki in his form.
Lucci's strength was illustrated by use of the Kamie Bushin, since in that form he was quicker but lacked the punch power of his huge form. This implies he's slower in his huge form, but weaker in the Kamie Bushin. So, clearly, there's some sort of power/speed trade-offs going on there.
As for Kaku, his Bigan is, perhaps by far, the most highly damaging attack of the whole series, even taking into account Ener's attacks. This is because the sheer weight of Kaku's neck muscles, and their density, not to mention the incredible speed of the attack and area of impact, probably exceed Gigant Pistol by a huge amount, and we should all remember that move nearly knocked out Lucci.
Follow this with the Amane Dachi, which was the most powerful Rankyaku, and Kaku's increased strength becomes apparent; I'm willing to say that in his Beast Man form, Kaku had greater strength than Lucci. Provided he had time to train his fruit, he could have surpassed Lucci in strength over the period they went undercover in W7.
Jabura didn't really seem to have that much of an increase with his form, but he had claws and bigger feet. He proabably was really strong too, but lacked the same speed penalty Lucci had since he wasn't as big.
@Fire Fist:
Others that were completely useless were Pierre's (Why would a Pegasus need a bird zoan?), Jyabura (He didn't even use any wolf moves, only Rokushiki), Funkfreed (An Elephant sword? What the hell?), and others.
Pierre was a bird that ate a horse fruit to allow someone to ride him. Jabura didn't really have an outlet for "wolf" moves, and Frankfried's one of those gimmick fruits.
@onemoment:
the SHs were just stronger.
Winning a battle does NOT meant one is stronger than one's opponent. All it means is one WON. Bellamy could have been a ton stronger than Luffy and we wouldn't have known, but Luffy beat him because he underestimated Luffy.
It's outrageously to call Sanji or Zoro "stronger" than Kaku or Jabura; if they weren't disadvantated, there wouldn't have been any purpose to the fight, now would there? Luffy was stronger than Lucci but he fooled around and almost got beaten.