"I find it a little incredulous that the bombers managed to get away with the "only going to make a bang in the terminal" excuse.
- They could've stuck the bombs in any bag and set them off check-in side.
- They didn't need to have suicide videos.
- They didn't need to disguise the detonators at all.
If they wanted to get through security, then they were after the planes."
None of which could be used to bring a guilty verdict. Remember that to bring a guilty verdict then there can be no reasonable doubt. Your points are all based on assumption, if you are making an assumption then you are not offering proof positive and as such there must be reasonable doubt.
Could they have caused death and destruction on an airliner? Probably. Were they planning to? Hard to prove beyond reasonable doubt.
The one thing that would have nailed them bang to rights would have been airline tickets. So the question is, were the security services right to pounce when they did or should they have waited to see if their suspects had booked tickets.
Also, whether or not their bombs would have done their job is really a moot point. They intended to detonate their devices. They believed their devices would work. In order to bring a successful prosecution for conspiracy to commit any crime then surely the important thing to prove is that the accused planned and fully intended to commit the offence, not that their plan would have actually worked?