Its not speculation if the manga has shown time and time again that a bigger rasengan = a more powerful rasengan. Minato's rasengan was both much larger than the one naruto used against the third raikage, and the damage it did to the ground is much greater than the damage naruto's does. I would almost say that it was equal to naruto's oodama rasengan.
Damage to edo tensei's are indicated by cracks, recovery smoke, and flying paper. The rasenshuriken did damage the third, but not enough to keep him down, hence the cracks all over his body and the regeneration smoke.
Naruto's rasengan damaged his arm hence the cracks at the area the rasengan contacted the arm.
There was no flying paper because that is indicative of heavy or deep damage.
Only damage to edo tensei ninja's is when they begin to regenerate. Ill upload images to end this discussion.
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These three images should keep you quite. Edo ninjas have cracks all over their body and face. Only when they are damaged do they regenerate. 3rd raikage didnt regerate, therefore he wasnt affected. Those cracks ive already explained them to you
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Btw naruto's rasengan is stronger, he was in km mode when he used it