A single 7th level spell does not a build break.
I have *actually* been considering dropping the SF: Necromancy for another mental toughness feat I know I know, I can hear Shade screaming at his monitor already. Having 2003 spell points and still just 32 charisma is just looking OH SOO juicy....
I don't feel that an evocation focus is quite worth spending a feat on, especially 2 levels of it for a sorc. Maybe if I had another feat or two to play with, maybe end game I will have it, but not this current point in time. The evo focus will only increase failed monster saves by 5% per feat, only marginally increasing DPS.
Bear in mind that this character is somewhat generalist yes. He is rounded out for being able to solo pretty much every quest in the game. Necromancy focus is for dropping casters and clerics before they can hit me with a command or other nasty enchantment, and cone of cold + fireball is for mopping up the melee type mobs.
I really RARELY use my firewalls, except for in certain quests with phasing monsters or ones requiring sustained DPS over time. I have found that Cone of Cold is my staple nuking spell.
And yes when the level cap raises to 16 I will be taking Delayed Blast Fireball and probably Polar Ray as my level 8 spell. Hopefully I can get my hands on a greater potency VIII one-hander early next mod. However, if they do me a favor and put MIND BLANK in the level 8 spell list, I will have a pretty tough decision.