Ah, but control and buff are considered superior to damage so what if I cast say grease then attack my now prone opponent and get an aoo if he stands and create difficult terrain for other enemies trying to close or true strike the same round I attack, and of course there's spell strike. You would think nothing of using power attack to take a -2 penalty to hit for a +4 to damage but a -2 to hit for a +5d6 or +1d6+5 and fatigue (no save) is a poor trade? I don't get it.
The tactic is making assumptions that all the steps work. Note that I advised
against Power Attack, unless you explicitly have a source of accuracy making up the gap, you don't want the damage more than you want the accuracy. Spell Combat is inherently high risk, the -2 to hit make your 2-3 melee attacks more likely to miss, attacks which, given your arcane pool, carry plenty of rider damage dice, there is also a need for concentration checks, which add another failure point, and whatever spells you're casting would have saves(not so good for a 6 level casting class, your saves are slightly behind just like your attack bonus is slightly behind). You also lose the extra attack from Haste and similar, which is a pain.
Spell Strike likewise, you're replacing a high chance of hitting with a weapon attack, which is worthwhile in 2 cases, when you are already certain to hit, or when the spell does little of significance on it's own.
Say for example, at level 8. You have a BAB of +6, and including race/enhancement items, are working with an Str of 20. Your weapon can be enhanced to a +4, but is more likely a +2 and +2d6 damage, and you can throw a Haste on(which, incidentally, is well worth using Spell Combat for if you started combat in melee).
This gives you an attack sequence of +13/+13/+8 [W]+7+2d6.
Spell Combat with a touch spell(say Vampiric Touch as the best one you can get at that level) for an extra attack converts the sequence into +11/+6 [W]+5+2d6 and +11 [W]+5+2d6+4d6, and you need to make a DC 21 concentration check at a bonus of +11 unless you did some fancy footwork.
Expected base AC at level 8(based on the CR guidelines) is 21, which means you go from 60%/60%/35% to 50%/25%/50%. This drops to 50%/25%/25% if you need to make the concentration check, though the check is significantly easier if you use a 1st level spell like Shocking Grasp(which gives you a 50%/25%/70%).
Each use of spell combat costs a spell slot. You want to make that count. If, however, you had the time(Arcane pool costs your swift action, as does most of the Arcana which augment accuracy) and resources(keep an eye on how much of your pool and slots are burning away per combat) to add more bonuses to your attack roll, the factors change, a +5 bonus to hit across the board on top of your arcane pool enhancement bonuses work, if you can somehow apply it with your given actions. Incidentally, action efficiency is one of the reasons I advocated Bladebound, it adds damage without costing actions using it's own arcane pool, while Kensai offers AC and initiative, early, as well as better weapons and weapon specialization(though it comes so late it doesn't really add a lot).
What you WOULD find useful on spell combat is movement spells and buff spells, neither which require that you cast from inside the opponent's threatened area, nor that you provoke a save and thus eliminating one point of failure. A -2 to hit and damage for all attacks isn't quite worth the trouble for an additional attack when you don't have a high to hit to begin with.
It's worth the trouble for a debuff if you can't outright kill the target with damage in two rounds, and can fire the debuff from outside their reach. It's also worthwhile for Force Hook, Force Hook Charge, Bladed Dash or Dimension Door(since it's part of your spell combat action, not being able to take actions may not apply until spell combat resolves), since you can get a full attack a round early.
