This is indeed a personal opinion as any answer here is. However with more serious gaming I do not believe that the issue is simply the ergonomic keyboards are poor for gaming, rather the problem lies in that I do not know of any keyboards that are both ergonomic and designed for gaming.
Gaming keyboards have a set of particular traits, they focus on latency, the resistance curve as you push down the key, the distance the keys move and how 'clicky' or 'soft' they feel. They tend to have large keys without gaps between them and the contours on the keys are often less pronounced than normal keyboards. In addition they also focus on allowing many keys to be pressed at once (known as rollover) which is useful in many games.
An ergonomic keyboard rarely considers any of these traits, rather focusing on the shape and spacing of the keys. This is not fundamentally conflicting with the goals of a gaming keyboard but I simply do not know of any keyboards focusing on both gaming and good ergonomics. In short, there is no reason an ergonomic keyboard cannot be a good gaming keyboard but I do not know of any which focus on the needed traits for gaming.