"Where is it compared? When have you used a gas engine, with same displacement, on same hill with same load?"
It's kind of a mute point. The exhaust brake has become a standard feature on HD diesels. A feature that works well and is a real difference maker.
A feature that HD gassers simply don't have. There is no comparison to be made.
We don't need to get into load, displacement or any other factor.
The gasser does not have an exhaust brake. Ultimately no exhaust break is a deal breaker and a major shortcoming of a gas engine