1. Why would this god create a system where if some of the 'first generation' mess things up that this god is helpless to fix it?
For all purposes, there is no real other way of going about it in a wise manner. Our actions effect others and generations that follow. One man change everything sometimes. The trial is that we can effect others. This is the hugest trial, although from one angle, our actions are just responsible over us and effect our souls and other souls don't get accounted for them, in another way, we influence one another. So our actions are not irrelevant to others.
2. I guess you can claim what these people failed to do is not on this god, even though this god is the one who created the infallible humans that messed things up, but you can certainly place the injustice on this god for deciding that millions of people not yet even born have to suffer because of mistakes made by other people centuries ago.
Yet there's hope in Quran and Ahlulbayt (a) and the Mahdi (a) and there's enough light for us to spread it and act on it.
It's bad, but there is till guidance and good. A lot of it is upon just a few humans, even maybe me included in those few humans needed, that all they have to do is their duty, and everything will fall to place. The problem is sometimes there is no helpers or people obeying God sincerely, just as Musa (a) said "I do not control over anyone except myself and my brother, so split between us and the people of transgression"
3. Worse yet, it isn't just the descendants of those in the Middle East who actually had the opportunity to witness these miracles, but failed to help in this god's cause who suffered. Even those who's ancestors lived on the other side of the world and knew nothing about this god being in the Middle East or its cause must suffer as well.
It looks bad on God but this the best way he can help.
Mohammad's (s) companions and generations of Muslims who were present till Imam Hassan Al-askari (a) failed the whole world except a few who saw the truth and helped it and some were maimed, others slain, others in jail, others had to leave their lands as fugitives.
Then Imam Mahdi (a) disappeared.
The crime is effecting the whole world. It's a huge tragedy to people of the skies and all people of Islam, the killing of Hussain (a), but also a tragedy for the whole world.
But yet everyone can follow truth. Do something about the situation.
We Muslims can severe the link to our past, and start fresh understanding, but will we do it?
Non-Muslims can learn Quran and Ahlulbayt (a) without following our scholars and making them the authorities on Islam with no proof, will anyone do it?
We all can help, it's not that we can't.
But for most, they need a push. Some need majority on the right path before they join it.
All I can do is my best. There's hope.