The Psalms that are written as prayers are actually prophecies. Psalm 83 will soon show you that if you doubt it.
The book of Romans talks about how the Holy Spirit helps us even in our intercession.
My point? It doesn't have to be "either-or" on these things (unless you have some interpretation agenda you're trying to force thru the text)
IOW, the Psalmist could have readily been led by the Holy Spirit to pray a given phrase/sentence/graph...and it could also thereby be a prophecy.
You are the one insistent that we carefully and surgically compartmentalize the two (not me).