Yes but why would Orochimaru train and get strong enough to take it from Itachi, when he only wants a strong sharingan and there are options? His goal ain't Itachi's sharingan but a sharingan, which is where this falls apart. He has options, Deidara doesn't for his grudge.
Orochimaru had plenty of connections to get some spare Sharingan from Danzo for instance. The entire point was to take an Uchiha's body. Orochimaru recklessly attacked Itachi and burned his hand by being struck with the vast difference in power. That was the one Uchiha directly in his reach yet he completely abandoned that option to groom his younger brother and dive into years of stress to put up with Sasuke's bs. He literally complained himself that all this is only because Itachi is way out of his reach.