Toni, that's just what I was going to say. My season is longer than yours but much shorter than what Porkpal or Zuzu have, and plants like salvia and spirea don't have a chance to get big. I think the heat and dry air also limits some of the plants that might be invasive elsewhere. Tradescantia stays small here because the ground is dry.
My "formal" bed has low growing groundcovers. The roses in the mixed beds seem to do better, and they share space with taller perennials. It might be that the formal area is a raised bed with dirt I paid for, and the other areas are the soil that was here naturally. I never ever expected the native soil to be so much better than what I had hauled in, but it is! It also might be that i have all my Hybrid Teas in the formal bed, and many of them do get bare legs, which i think are just ugly. Too many variables to make any real conclusions, but what I do know is I like the look of full beds, no bare mulch.
Our extension service has a fabulous rose garden maintained by Master Gardeners and Rosarians. They have the same roses I have, and there's no comparison! They feed the roses regularly, and spray for insects and disease. Everything was planted correctly, mulched correctly, and watered often. THey really are beautiful, but when they are not blooming, there's nothing to look at. My goal is four seasons of interest in every bed.
Other low growers that do not have extensive roots are purslane and portulaca (rose moss). Purslane is not hardy here, and I can't afford to buy as many as I want since it is usually sold in 3" pots for $3. THis year, I found a nursery selling 6-packs of it for $4, so I planted more. I may try to overwinter it in my garage and use more of it in the formal bed.