Of course you're right in general but the fusion triple product actually did increase exponentially, at a faster pace than Moore's Law, from 1970 to 2000. Then for a while everybody decided to put most of the money in a giant construction project in France that still isn't finished. Now we're partway back to the system of competing smaller projects that we had during the exponential period.

Lasers have also been improving dramatically. In particular the power of fast lasers has been going up exponentially.