This is indeed the typical mature size and shape for a Chinese Redbud, at least for 'Avondale'. It's normal for the foliage to only be on the upper branches, just as with any other tree, but if that aesthetic is unappealing, you can try some gradual rejuvenation pruning to get more lower growth. We don't know how well that will work, but you can experiment if the tree is too tall for you in that location. (Trees never really stop growing when "mature," but they can slow down considerably, especially as they focus more energy into reproduction over vegetative growth.)

A bit of occasional branch dieback is normal as well, though might be exacerbated by prior drought conditions or years with heavy rainfall (like in 2018, which some trees, like certain oaks, are still recovering or declining from, if the soil wasn't well-drained enough). Eastern Redbud is vulnerable to Botryosphaeria canker, for example, so Chinese Redbud might be as well; drought and heat stress (perhaps exacerbated by the nearby wall) tend to play a role in predisposing plants to infection. We're not certain that's the cause behind any dead branches you encounter, but it's a possibility.

If you want to try rejuvenation pruning, which has worked with Eastern Redbud that suffered some canopy dieback, you can choose no more than one-third of the oldest stems (trunks) to cut back any given year. Over a cycle of about three years, you can then gradually cut back all stems as new growth is taking its place. Those young stems and branches might need to mature for a few years before they flower, so overall the tree might flower poorly or not at all, depending on the stage of that process you're in, for several years in a row. Multiple suckers will probably arise from each trunk pruning, so you'd need to carefully choose which to retain as the new trunks and remove the rest to shunt that energy into the desired growth. You probably want to take any trunks down that you'd be removing as low to the ground as you can go without injuring other trunks in the process (a folding pruning saw is handy for such cuts in tight spaces), not a three-foot stub, though it's something you could try if you wanted. If enough light doesn't reach the location you prune a trunk down to, the amount of regrowth will be minimal, at least until the entire canopy has been reduced.

In our opinion, if you're enjoying the flowers and the tree isn't at risk of interfering with a utility, window view, or anything else uncompromising, then it's safer to just leave it as-is and enjoy its lush growth and abundant bloom. "Short-lived" for a tree tends to be in the neighborhood of 2-3 decades, but that doesn't mean a specimen of a short-lived species won't be appealing for even longer. Stress can shorten any tree's life by making it more vulnerable to opportunistic pests and diseases, so there are always exceptions to life span estimates. If you're okay with a risk of potential wood decay (should major pruning cuts not seal-over properly, since they should not be painted-over) and poor regrowth, you can try doing the three-step pruning process to reduce the entire canopy height and encourage regrowth from the base. As the new growth shades the base again over time as those young branches fill in, the tree will again become bare-bottomed, though that's a natural progression. Granted, 'Avondale' is compact enough for a tree to almost be considered a large shrub, but in either case, it's a plant with a tree-like, vase-shaped growth habit when mature.

Miri