You need both. And in my experience it’s rare that an engineer will have strong soft and hard skills. I have known exactly one person with that rare combination, and he has since started his own successful company.

Unfortunately the smartest and most component engineers I have known have nearly always come across as being arrogant. They have a very solid grasp of their domain and a strong skillset, but they also expect everyone around them to be at their level and instantly follow everything they’re saying. These people sometimes even have disciples who follow the philosophy of arrogance and engage in gatekeeping. I have concluded that while this is not ideal, it’s often par for the course.

Conversely, the best engineering leaders I have known (architects, tech leads, product owners, requirements analysts, etc.) have had really strong empathy and encouraged healthy debate while also making everyone’s input and analysis feel welcome and valued. Their technical skillset is not necessarily the strongest but they’ve usually been good generalists who could talk intelligently about something at a high level without having to know the technical details. These people have also been able to take those arrogant engineers and have gotten them to successfully collaborate with everyone from the junior devs up to management. A good tech leader really is just a good mediator.