Amelio simplified the product categories down to four. They were still full of garbage--Jobs made the real difference there. He got rid of all the trash peripherals and replaced the (many) computer lines with only the iMac.
Amelio failed to cut the printer/accessory divisions which were mostly just selling rebadged hardware from other companies. He kept the Newton division even though it was not on a trajectory to success (I say this as a long time Newton fan). He also kept around far more Mac SKUs than were necessary (Performas, education-only SKUs). That's all stuff Jobs cut when he came back.
Amelio had the unenviable task of righting a sinking ship. He didn't necessarily do a bad job at it but acqui-merging with Next and getting Jobs back was the best choice he made during his tenure.
In a way Gil probably would have done very well working under Jobs but once you are in the CEO seat, there is no chance of taking that demotion.