Regarding Aston Villa in the Champions League, yes they have really tried because even I didn't think they can get up to this stage of the competition, but the truth is, this particular stage might choke them but hey this is also football where anything can happen at any point in time. Liverpool didn't leave the competition at their own accord, they were eliminated and I see no advantage on them leaving at this stage, because it now this period that they were supposed to concentrate on the competition since they are 13 points ahead of Arsenal in the league with less than 10 games to go.
They are a dark horse that cannot be predicted but it is a good thing that is shown because at least for now only Arsenal and Aston Villa are giving a little face to the EPL in the Champions League competition considering several other clubs have been eliminated from the competition.
This happened due to the cold hands of Emery which is no doubt. He is always quite capable of bringing an ordinary squad to a level that cannot be predicted.
Previously he had also brought Villarreal to this phase and even won the Europa League so for now Aston Villa's chance as a dark horse under Emery's care cannot be underestimated even though in terms of squad depth they are certainly inferior to other clubs in the quarter-finals this time, it's just that big clubs don't seem to be able to underestimate them.