Aside from replacing the battery, which it's not worth doing until it drops to around 80%, there is not much you can do.
It should say underneath the % in the battery health tab that your phone is running at peak performance and if it does, there's nothing to worry about. If it doesn't, there will be a slider that allows you to disable any throttling that is stopping it running at its peak performance.
Because of the less battery capacityWhat makes you believe that this would happen with a loss of just three percent?
Your phone's performance won't decrease until the battery gets too worn to support peak performance, which theoretically shouldn't happen until it's below 80%, and even then you can turn that feature off.
No, that’s not what I was inquiring about. The past is dead and gone. He/she is looking at 3% less battery capacity and to even expect a slower device based on the OP is a bit on the paranoid side, to me.You're asking why he thinks apple does sneaky stuff? Probably based on past behavior.