Loki survived because he is a demi-god plus the goal was to close the portal. The Chitauri were cannon fodder which is fine. Transformers movies could do with more cannon fodder armies. That's something they tried during AoE during the Galvatron subplot but that just bloated the movie in my opinion. The 'bad guy ship' was just a ship and was not a key character which lessens the importance of the destruction. In addition, except for Thor (maybe Hulk too), the current Avengers core team are all human even if they are super. So the battles have to be appropriate to that. The army in TF1 identifies sabot rounds as a way of hurting/defeating Decepticons prior to any meeting with Autobots, sabot rounds in the movie are military issue munitions. This plot device only exists because of a need to pander to the armed forces. The Avengers may be overrated but it is still, unfortunately, superior to any Transformers movie to date which is a big shame. It is what happens when one property had a formula for critical success in place and the other does not.