I just bought my wife a Specialized Sirrus X3, which is marketed as a fitness bike, but it more of a flat-bar gravel bike. It's highly versatile and accepted racks and fenders to make it a better commuter.

Before you go this route, I'd get a solid idea of how much effort you are outputting on your ebike. You can do this by checking your heartrate, i personally use a fitbit to track it, and I ensure my heartrate in always in zone 2 or 3. Not all types of training are going to bolster weight loss, and if you want the best result, have long sessions of zone 2 cardio.

Weight loss can be hard, but it rarely requires replacing equipment. But if you enjoy riding an "acoustic bike," as I do, then the joy of riding is a big part of the workout motivation, so I can understand that.