I played around in Fatesinger a bit with my sorc. It's got some things going for it. My DCs were 1 higher on Evoc, 4 higher on all other spell schools than draconic. It gave me an extra 70 universal spellpower over draconic, and the "free" intensify adds another 75 spellpower to all spells for no extra mana. The free enlarge is crazy nice for anyone who throws DC spells. The MRR/PRR debuff is useful, though I wasn't seeing it impacting red names. And the arcane "memory" buff is very nice, enough to twist when I'm in Draconic. At the end of the day, however, +30% crit damage trumps all when you're sitting at a 93% chance to crit.
If you're DC focused, free Embolden and free Enlarge that you don't need to use a feat slot for would seem to be a benefit, but it's hard to ignore the huge DC boost in Magistar if you're purely DC. I think Fatesinger is more in play if you're looking for casting damage. The spellpower it gives in the cores adds up really nicely, and free Intensify for no feat slot is really nice as it allows epic eldritch, embolden, burst of glacial, etc. without needing to skip a feat for it.