The Taliban can be defeated, but their just isn't the Political will to commit the resources necessary to do it. That's the problem. There isn't even the political will to try and close the boarder with Pakistan.
The British experience in Malayia did not happen in a few years.

We are up against essentially a non-existant society in Afghanistan, weaker even than the original US Articles of Confederation that governed while the US Revolutionary War dragged on due to lack of the strongest support needed but not then possible from the original Congress in Philadelphia.

I still think a return to the monarchy for Afghainsitan, with tribal jiirgas working under same is more likely to work...although a modified weak Parliamentary system able to veto or check and balance a King might work, too?