@boiga:
DogPeng was mostly given Sanji's martial arts skills and not his strength. Sanji showed himself to be much stronger during his fight with Absalom. DogPeng was KO'd by a single shot from Absalom's invisible bazooka while sanji took down Abs with ease.
Well you have to remember the body is taken into account also. It's obvious Dogpen wouldn't be as strong as Sanji. That was why Ryumma could so easily beat Brooke. Ryumma had all of of Brooke's strength and skills, and also had a way stronger body.
Dogpen was probably the worst body to put a shadow like Sanji's anyway since the short stubbly legs weren't helping.
But even if the strength of the shadow's owner does trickle down into the person using the shadow, the math doesn't add up. One hundred men would not be cumulatively stronger than either luffy of Odz, so how did it make luffy stronger than the giant? The hundred men that Luffy absorbed couldn't have been much stronger than average either because otherwise the Rolling Pirates would not have been able to defeat their zombies.
If an army of one hundred men could not defeat Odz, how could they give luffy the power to defeat him one on one? Is there some multiplicative effect here that we don't know about?
Well I think it's basically going by quantity over quality. Lola and the others are most likely thinking "if we throw enough shadows on this guy he'll have the strength to take Moria down." So its adding all the strength of these shadows into one already strong person i. e. Luffy.
I mean you throw enough soldiers at a target they'll eventually win no matter how strong someone is. I mean look at Enies Lobby, had the Strawhats gone in there by themselves without any of the help they got they would've most likely been defeated. They could've beaten alot of marines but the sheer number of them would've eventually overcome them. That's why Zanbai wanted them to not fight. I mean for the most part the Strawhats avoided fighting.
About your second question, there's like a multiplicative effect, otherwise Lola wouldn't have bothered inserting so many shadows.