Well, I suppose you could 'cheat' like that. Still, even at 10 point spent, going with Foci gives a slight edge if you only worry about two elements (one defense, one offense).
Of course, you'll hit a brick wall with Foci at +6 ones, since you need something unwieldy to go beyond +6.
You only ever want to concentrate on one element, not two.
Example, wizard guy:
superb: lore, discipline
great: conviction
So he can have up to +5 bonuses from foci or specs.
He spends his 7 points of specialization and gets +5 spirit power, +4 spirit control.
That gives him 9 base power and 9 base control (or he could have 10 control and 8 power, or whatever).
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Hmm, now to consider whether that can be bested by some combination of specialization and foci...
We have a base control of 5 and power of 4.
Our free point of specialization goes into power.
We spend out first point in specialization for +2 control.
So not he have a base control of 7 and a base power of 5.
Now, we have 6 points left to spend on foci, giving us 12 points of foci bonuses.
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1st, we try to match or exceed the specialization only guy:
We need +4 offensive and defensive power, and +2 offensive and defensive control to match the power 9, control 9 of the specialization guy. So we can match him, but we need two staff sized foci, loose out on some minor bonuses (+3, +2, +1 to other elements), and have foci that can be taken away; all-in-all a horrible deal.
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Next, can we imbalance ourselves in offense or defense with foci?
We can make a +5 control and a +5 power foci (the limits of our lore) and end up with control 12, power 10 (or, with a few minor changes on our character sheet, control 11, power 11 if we want instead), and we still have 2 foci slots left, which should get us to control 7, power 7 in our neglected choice (offense or defense).
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So, foci are weaker than specializations, but do allow you to unbalance yourself toward offense or defense. Since enchanted defensive items are usually a better defensive option than evocation blocks, an build that uses enchanted items for defense and foci to gain quick offensive power is probably the current best build.
Looks something like:
Superb: Lore, Discipline
Great: Conviction
(7 points of refresh to spend)
2 points spent for a +4 crafting strength foci (to bring base crafting strength up to it's maximum (lore x 2) of 10 (includes +1 from free specialization)
1 point spent in evocation specialization (control +2, power +1; base now control 7, power 5)
3 points spent on focus items (+5 offensive control, + 1 offensive power; single focus, staff sized)
and 1 point on enchanted item slots, giving you 2 power 10, 3 use items for defense.
So you have:
Offensive: control 12, power 6
Defenses: two layered power 10 defensive items, or power 5-7 evocation blocks if you don't have your items)
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Final comparisons:
Specialization guy: (no foci)
Offensive: control 9, power 9
Defensive: control 9, power 9
Focus guy (Offensive spec): (2 staff sized foci, 1 small foci)
Offensive: control 12, power 10
Defensive: control 7, power 7
Enchanted item guy: (1 staff sized foci, 2 ring sized enchanted items)
Offensive: control 12, power 6
Defensive: 2 power 10, 3 use defensive items
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Note that this neglects your 4 points of 'free' foci, so all of the builds are slightly more powerful than this.