Poor venting is not inherent in the technology. A diligent installer can run a duct from the oven to the outside just like we do for gas boilers. A diligent building code can even make it mandatory. The lack of gas ovens (and selection thereof) in Belgium is not likely a consequence of concern for toxic gases, because if it were, then gas boilers (which burn far more fuel than an oven would) would be far less popular than they are. So what is your theory on that difference?