I think God can, and probably does, answer prayers for strength or courage in the affirmitive. Things that make you a better person. That would serve a purpose important to Him.
But the conditions of this sinful world are such that bad things happen. They happen to everyone and they always will unless and until the prophecies of Revelation are fulfilled and there is a final judgment.
But I'd never see a doctor if I thought the power of prayer was sufficient and effective. None of us would.
That's sounds logical, but faith and prayer aren't logical. The people that did this study came to a logical conclusion, but only if you look at prayer as always being answered according to your wishes.
I think God gives each person what they need because we all are individuals. He made us that way. Some people need more at different times than others. It sounds like you are one of people that need very little affirmation from God. Your faith is sufficient to carry you through this life. Others need more and God reaches out to them occasionally and gives them what they need to carry on.