Your second sentence is negated by the first.
Your argument seems to be "might makes right." Just because a being has the power to do something and we do not have the power to resist, does not make it just. I can pull all the legs off a spider without killing it. It cannot stop me. Does that make it just?
I'm not saying might makes right. Right makes right. Our notions of right often are at odds with God's notions of right. He's the ultimate arbiter, not us. How could it be us? There are thousands of different worldviews out there with differing versions of morality. Why is one the right morality to the exclusion of others? Either there is no absolute morality or only God's morality is perfect. If there is no absolute morality, then any talk of right or good or better is silly, as none of those terms can be true in any given situation.
What you've just presented is one leg of The Euthyphro Dilemma.
"Is that which is good commanded by God because it's good, or is it good because God commands it?" [citation omitted]
1. If that which is good (or just) is commanded by God because it is good, then there is a standard of goodness/justice which is above God, and which God himself must adhere to, rendering God just the messenger of what is moral and not the standard.
2. If that which is good (or just) is such simply because God commands it then you have nothing but an arbitrary morality, a divine dictatorship (a cosmic Kim Jong Il), at which case nothing is truly moral or just because this dictator could change his mind at anytime (kind of like a mafia boss). If this option is true, how could you ever know (or judge correctly) that God's commands are good? HINT: The answer "b/c the bible tells me so" is not sufficient b/c there are lots of religious texts that say otherwise - nearly all of them are self contradictory - and no religious sects can agree on theology anyways.
Now if (like many Christians) you attempt to argue that there is a 3rd option (i.e. - that what is good/just represents "God's eternal unchanging nature" or something like that) you still haven't solved the problem. God's "nature" in the bible is often depicted as quite contrary to what is good. For example, is murder contrary to "God's nature"? The bible depicts God commanding, endorsing, and performing the termination of human lives all throughout the bible (aka - the Amalekites, the 42 young boys mauled by bears, women and children, etc). Is that moral? Furthermore, this answer is circular. What standard are you using to determine that God is moral, just, good, etc? If you refer to the bible, then all you've done is appeal to...God (again). So saying "God is the standard of what is just" is no different from saying, "God is the standard of what is God".
I'm sorry to have you tell you this but this view has been falsified. It is irrational nonsense and it should be abandoned in exchange for better reasoning.
False dichotomy. Morality is such not merely because God relays and commands it but because God himself is good and moral. As the creator of everything, his goodness went into his creation, and the original creation was perfect and not fallen. Since he gave both angels and mankind free will, however, and since many angels and all of mankind fell, this world does not exude the perfection and morality that God started it out with. Moreover, just because God could change his mind in the sense that it's within the realm of possibility doesn't mean he's going do. Indeed, he won't, because it is not in his nature. So the mafia boss analogy is, well, terrible.
Now when you claim that God's nature in the Bible is often contrary to morality, all you're doing is using your own standard for morality instead of someone else's. Millions of people probably agree with you, and millions of other people probably agree with me: either God's recorded acts in the Bible are moral or immoral, depending on which camp you're in. But why and how can either one of us be right?
Oh, you've got specific examples you want to discuss: God commanded people to die at various times in the Bible, and that can never be moral, right? Not necessarily. Wouldn't most of us, if we could go back in history and kill Hitler as a child, for example, do so, knowing what we know now that he'd grow up to do? Probably. Isn't it immoral to kill a child? It would seem so. But only a time traveler from the future would have the knowledge of what evil that child would bring into the world. If God is omniscient, he knows what evil the Amalekites, the 42 young boys, etc etc would bring into the world if they weren't permitted to continue living. That's harsh, but it's also reality. God could have been preventing much worse things from occurring via such judgments, which we simply don't know about because he prevented them from occurring.
In sum, you presume to know better/best. All it boils down to is you imposing your morality on God's conduct. If God is omniscient and infinitely wise, that's a silly endeavor by you, because we don't know all the other alternate realities that could have arisen.