For internal stuff you’re absolutely correct - but using “main stream” design language (the current trend of rounded 3 column AI layouts, corporate Memphis, skeuomorphism, stock photos of help desk workers, wordart, etc) that isn’t unique makes your brand forgettable. Sure it was mind blowing when it first came out but it quickly loses its uniqueness and starts becoming a sign of crapiness/scaminess/enshitificarion.

Your users will never make it to your no-nonsense backend if your marketing is completely cookie cutter.