Re: So much money wasted
"Especially since the easier way of destroying these 'terror groups' would have been so much cheaper"
If you want to do the job properly and get rid of the poison at source, level Saudi Arabia and consider doing the same to Pakistan - at the very least ISI HQ and anything to do with the government or military. To show good faith, as someone suggests above, cut all funding and diplomatic support to Israel too.
The Saudi's get away with almost zero criticism, because we're addicted to their product, but since at least the early 80's they are the main driver of most of the nutjobbery we see today where Islam's involved through funding and ideological support. When governments say "foreign funded Imams", they invariably mean Saudi funded; almost every mosque that has been fingered in the UK as a source for extremism has Saudi money sloshing around its books somewhere for both construction and ongoing funding. The most depressing thing for about the Saudis perhaps, is that it really does seem to be motivated by the desire to push an especially vile version of religion on everyone else at any cost.
The Pakistani 'terrorist' groups fighting India on the borders in Kashmir and behind attacks in Mumbai etc are all funded with money channelled from the Saudis through Pakistan's Inter Services Intelligence, who seem to operate as a law entirely unto themselves - certainly beyond the absolute control of politicians and to a large extent the army. The biggest possible error after 2001 was to treat Pakistan as useful allies who could be controlled and not to deliver on the threat to send them back to the stone age.
Until those two are put back quite firmly in their box, one way or another, this crap will just go on and on, however many Afghans take up farming.