Maybe straighter than you personally would run otherwise but dead straight? I think if you look at the form of top runners there would consistently be a small bend at the knee when the legs are bearing weight. Too much bend would be bad but that doesn't mean no bend. I also don't think we are particularly great at sensing exactly what our bodies are doing while running. Maybe they just feel completely straight. Take some videos, maybe your legs are straight, when they are under you, but you'd be the exception and I can only think that would make somewhere more injury prone - maybe the knee?

The other thing is that if you have an injury history in a specific part of the body then we can shift to a way of running that helps there but taxes somewhere else. That might be a price worth paying. But it doesn't make it the right thing for everyone. No idea if that applies to you.

ETA the straight in the video means overall posture and bent means bent at the waist, for instance. It doesn't mean the legs.