The reason why CCM choose the G450X motor is probably due to the fact they got a good deal on the old-new-stock that can pass emissions, hence why the bike is retailing at ~7000 GBP. Simple economics. They did not choose it because it was the best motor, most fuel efficient, and etc. They are getting a lot of performance for very little buy in.
How good, or how you perceive how good the motor is, is up to you and your experience. If you want to compare power performance in numbers and fuel injection and throttle response, you may want to turn around, and turn your monitor off.. They squeezed a lot of juice out of the G450X. Compare the power on 09 vintage motors, and the BMW wins hands down..
The G450X is not the most fuel efficient motor, and the tranny configuration is not best suited for extended trips (in the G450X configuration and chassis). The oil capacity is also not very well suited for extended trips.
The G450X was intended to be raced, trashed, and ridden hard, with occasional enduro here and there. The entire bike was built around this engine for this specific purpose. The bike is an overkill for your typical gravel runner adventurer.
Back onto the subject, I wonder what is the sprocket configuration they selected, and if they made internal changes to the transmission. With such major change to the chassis, it will be a shame to not address the motor to match the chassis and characteristics and the purpose it was built for.
Learn to ride. Ride to learn.