Turns out that if they're unusable by LLMs they're likely unusable by human devs. If you follow sane clean coding principles (like not having godclasses) it turns out coding agents (and humans!) can understand and navigate your codebase, especially if you use recognizable patterns, even with very light documentation.
Agree, agentic coding seem to have shifted the trade-off about over-engineering, I found clean architecture is a good practice for coding agent, so every task have a clean and limited context, only a few directly connected classes or interfaces is relevent to any local modification.