"He even miss identified his finches."
So? Is that the best you can do? He wasn't a bird expert. MOST naturalists would have misidentified them too. Show him a beetle and he would have been in his element.
True, but in general his labeling of specimens was quite good. And the extent of the collections he made were HUGE. Almost unbelievable for one man (albeit with servant most of the time). Just the strenous physical aspects involved -- climbing up and down sheer Andean peaks, manually pulling supply barges up South American rivers, galloping across the Pampas with half wild gauchos, carrying up to 70 lbs of water on trips to the interior of islands in the Galapagos, etc, etc, etc... It's almost unconceivable to a modern man what Darwin (happily and with little thought) endured making his collections.
Besides, Darwin proved his acumen when he got home. He know exactly who to give his finches, and other birds to work up in England, and thereby got the indenifications corrected almost immediately.