I think that's a reasonable criticism, but I'm more optimistic that there's value here for two reasons. One is that even a "basic proportional" level of control

I think that's a reasonable criticism, but I'm more optimistic that there's value here for two reasons. One is that even a "basic proportional" level of control is under-used, and most practitioners don't even go that far into analyzing the dynamic behavior of their systems. The other is that I think that fixing "local" behaviors where systems are linear enough and time invariant enough is likely to have a lot of value. Many of the "hold down" loops are relatively local effects. You're right that a lot of the techniques of classical control theory (both continuous and discrete-time) are hard to directly apply in a distributed systems context today. I do think there's a lot of value in the patterns of thinking, and that future research along those lines is likely to bear fruit (or, at least, be the genesis of better-suited techniques).