He was negligent in management, leading to company losses.
Tips
grammar
Pattern: 疏于 + verb/noun, "to be remiss with respect to X." Always carries a faintly accusatory/self-critical tone. Common collocations: 疏于管理, 疏于防范, 疏于照顾, 疏于联系. Never positive - you can't 疏于 something good.