Comment by agos
the "being grumpy" or being able to recognize problems is why during technical interviews I always ask the candidate to name their biggest complaint about a technology they know well/love/mentioned earlier. This to me is a great signal especially for mid seniority engineers that they are aware that things could improve
If they can't complain they either can't tell what's wrong or can't gain the courage to say what's wrong. Neither is a great quality, though the latter can be heavily influenced by company culture
But I also think how an engineer complains is important. It gives good insight into how they think.