I used to run an aluminum flywheel. For a slightly modified type application in our cars I think they are fine. I wasn't making any sort of "serious" power, but I had a full weight car and a decent amount of torque for a 2.2. I daily drove the thing...parking lots, stop and go, hills. This type of driving makes lots of heat. I also tried to drag race it (street tires). I would start the night with lower rpm launches (and bogged badly usually) and work my way up to higher rpm by the end. We had very long wait times between runs (a lot of the time an hour or more). I would always end up having the clutch slip on my by the end of the night. I burned the crap out of that flywheel.

Just like brakes, the flywheel also acts as a thermal heat sink. Aluminum may transfer better than steel, but steel absorbs more heat. Because there is a contact issue with these flywheels, the friction surface ends up absorbing all the heat it can before going over the operating threshold of the clutch quicker than it can transfer that heat to the aluminum part. More contact will certainly help, but due to the different expansion rates of the materials, improved contact at elevated temps will prove challenging. A paste would be something to try as they are deigned for elevated temperatures, BUT it cannot go liquid until over at least 1500*F. I propose a dead soft copper or aluminum gasket between the two parts. This would allow for the different expansion rates while also allowing contact to remain because it deform to the needed shape.