Houserule out the "Control" aspect from the spell.
The problem with the spell isn't so much that it calls in powerful monsters, in my experience. It's that it instantly gives you powerful but obedient slaves.
Calling in a Solar or similarly powerful creature isn't something I would like to cut from my D&D experience. What I would like to cut out is that any random Wizard with 9th-level spells can call in a Solar, tell it to make a sandwich, and it goes "yes master". There's no defense against this mind-control for the Solar, no saving throw, no action requirement, just control by the caster as soon as the creature is through the Gate. And that allows shenanigans, increasing the caster's ability scores being the least of which.
Now, if that control were removed, it would remain a powerful and supremely useful spell. You can still call in a Solar when your party is fighting a Balor, I'm sure the celestial would be thrilled to join the fight. You could call on it for advice. You could even ask it to increase your ability scores, which it might, could you convince it your being slightly more intelligent/strong/quick/whatever is a worthy use of its Wish ability. You just can't make it do things it ordinarily wouldn't do, by virtue of the Gate alone.
As a bonus, I'd say the spell now has far more narrative potential. "YOU DARE SUMMON ME, MORTAL?"
Be an Incarnate or Totemist
Looking at the incarnum handbook, your stats line up perfectly with their priorities, it can synergize well with a dip into swordsage (lucky you), and is an interesting and flavourful route.
The only trick is that the book doesn't explain itself well, so an amount of research reading the explanations in the handbooks (incarnate handbook + incarnum handbook + swordsage handbook + Totemist Handbook) is clearly indicated. Beyond that, it fits your requirements perfectly.
Beyond that, the fluff of an animated construct armouring itself in soulstuff just begs for plot, which is, itself, interesting. Your first level of swordsage is an interesting dip, as it provides skills, stances, and attacks that can provide some absolutely fascinating synergy with your invested soulmelds. You'll have to spend time working through the combinations, but it'll provide character-career long flavour and moves that will direct how you spend your essentia.
Unfortunately, you will want to plot out your character's build out to the conceivable end of the campaign. You're integrating two of the later and extremely fiddly systems (for the perfect trifecta, dip into binder just to watch your own head explode.) But, with enough research and preparation, this fits your requirements nicely, and provides a serviceable tier-3 character dripping with interesting questions.
In terms of integration, you'll actually want to advance swordsage more than you might expect. The Diamond Mind school that the swordsage has access to is concentration/constitution driven. The incarnate has concentration as a class skill, and by taking advantage of the clause that notes that half of other class levels go into your initiator level, there are some cute tricks. Specifically, you want swordsage 2 after you take 4 levels of incarnate/totemist, giving you access to third level maneuvers, all of which can be diamond mind, allowing you to apply concentration to many of your saves and damage rolls.
Ask your DM if you can retrain to have the following maneuvers:
- Moment of Perfect Mind (Swordsage/1)
- Sapphire Nightmare Blade (Swordsage/1) -- this will be your primary attack, since flatfooted can do quite a lot to help your accuracy. The full-round action to reset sucks, but... what can you do?
- Shadow Blade Technique (Swordsage/1)
- Distracting Ember (Swordsage/1)
Choose your stance based on your intended incarnate build and this guide. Your other 2 maneuvers should be a function of your intended build as well, chosen with an eye towards meeting prereqs.
Dipping back into swordsage at level 6 allows you to cherrypick other diamond mind maneuvers and stances, which will neatly complement your incarnate. While it's likely going pure incarnate is better, there's no reason to not mix it up once you've fallen down this path.
Best Answer
Pazuzu's Wikipedia article reveals his motivations.
The big picture is in the goals section:
So, he grants wishes to tempt good-aligned people into doing bad things. Simple enough. But how does it work?
The details are in the Cult of Pazuzu section:
(some formatting added for readability)
This is essentially the way the scam works:
Pazuzu appears to a good character, and grants them a wish. The wish is entirely above-the-board, with the only stipulation being that the character promises to spread Pazuzu's name.
While this isn't a binding contract, note that Pazuzu has already read the subject's mind. He won't appear if his scam won't work. For example, because:
The subject knows Pazuzu is a demon.
The subject fully intends to disregard any conditions on aid granted to him.
The subject knows about the scheme.
The subject intends to harm or trap Pazuzu.
As more people learn about the wishes Pazuzu grants, he subtly makes the outcome of the wishes more and more evil (but still effective).
Eventually, he has a big cult who are dependent on him for success, and have accepted some morally questionable outcomes from their wishes.
He reveals himself to the cult as a demon. He demands that anyone who attempts to repent be tortured and then sacrificed to him.
Pazuzu leaves the now thoroughly evil cult, and goes in search of new victims.
What does Pazuzu get out of this?
Followers on the material plane, in the form of the cult.
The corruption of good characters to evil characters (eventually).