Every preacher of the Gospel has their own style and own way of proclaiming the Good News of Jesus Christ. There is no better way and sermons can be engaging and effective in every style. In fact, I sometimes use different styles of preaching just to shake things up for the congregation and for me.
My default style is to begin right away with the sermon and to not end with a prayer/blessing or an amen. To me, the most important parts of a sermon are the very beginning and the very end. The beginning of the sermon sets us up as the gathered community to hear the truth of God’s word. The ending is what I want you to remember.
The amen at the end is your job. Amen is a sign of appreciation from the gathered community. It is not an announcement that I am done. You may or may not want to give your appreciation to a particular sermon. Maybe you don’t agree with what I said at all (don’t say amen). Maybe you didn’t understand a thing I just said (don’t say amen). If you appreciate what you heard in the sermon, it is your privilege to add your amen (say it loud and proud).