Liara showed them the blue prints when Shepard meet them after Mars they were well aware of the project.
My bad, you're actually right about that one. Still, if their Prothean beacon contains so much data that Asari overlooked Vendetta during millenias, then I can believe it's the time they needed to sift through it, by "process of elimination, mixed with a little desperation" to just find hints to the Crucible and Catalyst in there. By the time of the mission on Thessia, their scientists were probably trying to hack Vendetta. Not that they would have succeeded. With the Reapers on the verge of attacking, they certainly felt they were out of time to do that themselves and preferred to admit having a Prothean beacon and hope Shepard could extract it. That wouldn't have happened sooner anyway, because of dumb story contrivance. Still, the majority of the Asari population wasn't aware of any of this.
The crucible was pretty much ready by the time the reapers attacked Thessia had they shared the beacon before then a lot lives could've been saved and the asari might not have lost their planet.
No, as mentionned by Vilio1, the Crucible was still under construction during Thessia. The only thing that would have saved more lives, is if Cerberus, humans, hadn't stolen Vendetta.
The asari have the largest economy and the best diplomats they were needed at the the war summit but backed out when the krogan got involved. Victus sated that more people would die if they didn't try to form an alliance with the korgan the asari could've helped with the process.
I will repeat myself, hindsight is a wonderful thing. There are a lot of events that could have been avoided with what we know of the story once we finish the game, but that's not how the story goes, and even less politics. They backed out because they felt there was too much bad blood between Krogans, Turians and Salarians and didn't believe they could solve this. Can't really blame them, there was a lot of bad blood and they couldn't have done anything anyway.
They asari withheld a prothean artifact that contain vital information to the crucible that could've ended the war earlier had they shared it.
See above. The Asari leaders didn't even know what the Catalyst was, which means they were unable to hack Vendetta. They didn't know it held such vital information, and it still wouldn't have ended the war earlier as long as Shepard didn't come along to activate Vendetta, and Shepard was quite, quite busy until then.
I never did absolve the Salarian leadership the Salarian its worth noting IIRC it was certain elements of the STG that acted on their own and the asari never did front up to their mistake as Shepard was never allowed to point it out to the councilor.
What is the point of pointing it up? They know the situation is f***ed up and everyone's screwed (by a human faction, need I to repeat?). Do you really need to rub it in? What is that supposed to achieve? I for one am glad it didn't happen. That would have been one very childish and a** way for Shepard to react, even for a full renegade Shepard. Even full renegade Shepard recognized where the real blame lies: Cerberus. Besides, when it comes to pointing fingers, humans would have much more to feel guilty about if the blame for the actions of a few of them had to be reflected on the whole species.
The Asari had more time to act before the Reaper's got to their territory yet they wasted it and to be fair Hackett and Anderson did what they could to prepare for the reaper's to the best of their ability given to politics they had to deal with.
No. Their borders were threatened at the beginning of the game as well, like all the other species. That means they had to fight off Reapers, by themselves. If they managed to hold off Reapers from Thessia so long, they didn't waste it. If not, Reapers would have destroyed the Prothean beacon long before Shepard even reached Thessia.
If an Alliance Admiral and the (possibly) first human Councilor couldn't convince the rest of the military to better prepare for the Reapers, that means Alliance commend was as faulty of not heading Shepard's warnings as other species leaders. Political leaders in this game are all portrayed in a very bad way. Asari political leaders are no exception, but the population they represent are not guilty of their mistakes/misdeeds.
I do appreciate you made an effort not to start all your answers with 'except' and 'again'.