I don't know the suite of 3E or PF feats very well, but I would have thought feats that boost save DCs are at least passable choices for a decent wizard build.
I'm pretty ignorant of PF feats, but they were an alright choice in 3.5. The thing is, I'm pointing out that you've put significant resources into this build (40% of your feats) and you're still at about 50/50. And that it only gets you a minor effect compared to what you think (a charmed monster, rather than a dominated one).
Where in the Charm rules does it say the target has to be non-hostile? Is that part of PF? In 3E, all that matters it that you not threaten it.
Don't skip around between PF and 3.X, please. That'll make certain bits about Charm confusing (like, say, what Friendly means). Both have an SRD we can check.
Also, it doesn't say it has to be non-hostile. But I'm betting that if it is, it finds you a threat on some level. Maybe not (I could see that in certain situations), but I think even beginning to cast a spell might put it on edge (or make it feel threatened).
A hill giant has a speed of 50'. The range of Charm Monster for a 7th level caster is 60'. So it doesn't seem to be that hard to engineer to be within casting range, but outside melee range, of the giant, run the risk of a thrown rock (definitely the giant's less impressive attack) and then cast your spell.
Again, I could see you even casting a spell making it feel threatened (who the hell is this tiny magic man, and what is he doing? He's not just a peasant). And sixty feet isn't that far to the hill giant. That's one move action and then a standard to attack (10' reach). Or a charge (or one partial charge, in a surprise round). Or a rock, as you've said.
But again, if you cast, and he hears you, I could easily see a hill giant getting defensive (and feeling threatened) before the spell is cast.
I don't see how a Chaotic Evil giant even has allies - its leader, for instance, "lasts only as long as he can thwart attempts to topple or assassinate him". And a 6 INT, 10 WIS, 7 CHA creature looks pretty manipulable to me.
They explicitly band together. Some set off alone, but that takes me back to the niche situation you've found yourself in. If we change this "random" CR 7 encounter to, say, a ghost or a flesh golem, how good is your Charm Monster spell going to be? How helpful are those two feats?
Like I said, you've crafted a fairly niche situation (non-hostile hill giant against an enchanter specialist that are met alone so that their buddies don't attack, and you win an opposed Charisma check as a Wizard [no retries] to allow you to do something that I think is against the rules [fight its allies for you]). If we change it around to other niche situations (like fighting that flesh golem or that skeletal cloud giant), then your character looks way worse off.
You can argue balance problems, but your point was that preparing save or die spells wasn't particularly risky. I'm pointing out that even inside of your niche situation, it's still pretty risky, and it's not nearly as powerful as you make it out to be (I even quoted Charm rules for you... it may not even see your allies as okay). And, of course, outside of your niche situation, the save or die spell, the feats, etc. are a waste for that encounter.
So, I'll say it again (even though I just did), you can argue balance problems, but it's probably best not to argue that save or dies aren't risky and then throw out a niche situation (that seems to favor this Wizard very well). It's just not accurate.