I am a big fan of full disclosure, so let's not go overboard with Maui wildlife expectations. Turtles are rarely seen at Molokini, Lanai and Molokai. Turtles are nearly guaranteed on shore dives and boat dives along the Maui Coast, except perhaps the Carthaginian artificial wreck. Eagle rays might be seen on 30% of those same shore and near coast dives, but more likely on the Carthaginian. Manta rays are only around 20% probable, unless you make dives "timed" to see mantas.
A good guide can increase your percentages
PS - there are very few divers with equal experience in both islands that would claim the experiences will be identical.