Maybe not enough sun? It's the only thing I can think of that would explain all 3 of those not performing right. Rust is a problem on hollyhocks but they usually don't survive long enough to bloom in that case. Some types of yarrow need to be divided yearly to bloom well, so maybe try that. Delphiniums will benefit from supplemental water and feeding, but I would think the compost would be enough. It'd be worth trying more food and water next year to see if that helps.

You don't say how much water you used and I'm guessing that's the problem. You can't do much about it this year except think back on the results of the rainstorms on growth and bloom and also check with your finger to see if the ground is wet an inch or two below the surface - that would tell you if you had given them adequate water. I had yarrow that gave very little bloom but it didn't receive the deep watering that the thriving hollyhocks did in my garden. My hollyhocks are at the back of a deep border and fight their way up to the sunshine. Have you checked pH in the soil to see that all is okay (beneath the compost)?