I obsessively researched pools for my project and your concern is a fairly common complaint. Many people are uncomfortable with 12" step height when the pool is empty because 7" to 8" is standard outside a pool (like indoor stairs or patio) and they have to work much harder than normal.
However, you have to remember that when the pool is full of water you weigh less. Walking in the empty pool doesn't give you the proper comparison.
If you have any friends with a pool or access to a community pool you should go visit and do your stair tests with water. It may help put your mind at ease or confirm you need the re-work done.
12" is within standard from what I have read....but it is your custom pool and you can change as needed. People with bad knees or older in age may prefer an easier step height.
Have you considered hand rail type system as well? We are putting boulders next to our stairs so people can have more stability as they enter/exit