I would be extremely happy to be proven wrong! I love using agents for exploratory prototypes as well as "rote" work, but have yet to see them really pay off when dealing with existing tech debt.
I find that the flaws of agentic workflows tend to be in the vein of "repeating past mistakes", looking at previous debt-riddled files and making an equivalently debt-riddled refactor, despite it looking better on the surface. A tunnel-vision problem of sorts