The fallacy in that argument is that Russia is doing its war-crimes right now at this moment. What US did in Iraq was far less bad, and most importantly whatever US did in Iraq they stopped doing. But Russia has not stopped bombing Ukraine. Therefore, at the current moment, we must condemn Russia for what it is doing now, not US for what it did long ago and stopped doing.
And even if it was true that US was and still is as bad as Russia then so what? That doesn't give Russia the license to do war-crimes. Two bads don't make it right. Hey, I may be bad, but what about Al Capone? He was much worse than I!