I'll continue monitoring and report back as needed. Thank you!

This is reassuring, thanks for weighing in. I'll stick to my current regimen of watering every third day and see how they turn out. Fingers crossed!

4 hours is barely enough sun.

Yeah, I knew this would be an issue, problem is I'm on the northwest side of a duplex, and the short stretch of southwest-facing facade that I have are my driveway and garage. Only about six feet of my mulch bed wraps around to that southwest side (and it's already occupied by other plants), so for now, all my veggies are on my (northeast-facing) deck, but since they're all in containers, I might repurpose that little stretch of southwest-facing mulch bed, and I could potentially line my driveway with containers. The other caveat is that my driveway is slightly sloped, so... definitely not ideal. It just so happens that all the veggies I'd want to grow (tomatoes, peppers, cukes) love sun, and my physical environment is oriented the wrong way to maximize daily sunlight.

Over the last couple weeks we've had a few chilly nights w/ lows in the 40s—nothing crazy, but below average for this area this time of year.

The thought has crossed my mind to rip them out and plant something new in their place, but I figure since they're already in the ground I'll see what I can do.

Here are some close-ups of the purple leaves, top sides first:

The bottoms have black specks:

Even the green leaves have the black specks on their under sides:

Does this look like infection to your eye?

For what it's worth there are also branches w/ no foliage and other branches where the leaves have completely browned and are crispy to the touch, like they were cooked in an air fryer: