Because if the big nuke is per encounter now, the normal fights have to be hard enough to justify using it.
The big bad dragon can't be that much harder than the average adventure group, because how would you beat it without that special spell that you kept in reserve all the time.
Eiher that, or every fight except for the big bad dragon is spam that can be nuked away easily.
Or there is no big nuke anymore. Just lots of firecrackers.
Please correct me if I misunderstood or overlooked something.
My guess is that the per rest spell empowerment function is how you will get the "big nuke" effect. otherwise mormal cast are all scaled as "fircrackers"
Per Sawyer:
Aside, weren't long cast times what jacked up the Chanter?