I would suggest the families of the two dead aircrew might have expected any allegation of negligence on the controller's part to be thoroughly investigated and, where a prima facie case existed, prosecuted.
Pre-trial delays can occur for a number of reasons, not always of the prosecution's or police's making. Jurisdictional, defence and other issues can often cause delays. Did the Judge Advocate make any observation at the end of the Court Martial, regarding the time it had taken for the case to come to trial? A judge advocate will normally criticise the police and prosecution in open court, where he feels they have not acted expeditiously.
Where a defendant is acquitted, his costs are normally met by the court.
As for senior officers 'pushing the case', there could be no prosecution and trial of this case without real evidence. The fact this Court Martial lasted 22 days would tend to suggest there was a case to answer.
I have no axe to grind in this matter, but do not feel that any great injustice has occurred.