Naturally this sort of issue has been reported in the past: https://bugs.chromium.org/p/chromium/issues/detail?id=672625

From the comments on that bug there's other ways to detect devtools (including timing attacks), and it wouldn't be worthwhile to track down every possible case.

As someone who uses devtools debugging a lot I think that answer is reasonable, these kinds of shenanigans mostly only slow down and amuse expert debuggers.