Personal opinion, I don't think it's a "common" experience for guitarists to have a hard time strumming with a pick. My own experience? I found it about as difficult as drinking water.

So I'm having an empathetic stab in the dark here, as my experience has been different. I can certainly strum with either my fingers or thumb for effect or tone, but much prefer a pick most of the time.

Have you tried every different type of pick material, thickness and size of pick? It does make a difference, especially to string attack and consequent tone and rhythm.

For strumming tone on an acoustic, unless wanting muted pianissimo, nothing I've tried yet beats a Dunlop nylon pick of the thickness e.g. .38, .46, .60. .73 selected for the desired tone. Give a .38 or .46 a try. I suspect you'll be surprised. Soft attack is unavoidable with a .38 and it glides over the strings with rhythmical fluidity for wont of a better phrase coming to mind.