Tyrion’s only real military achievement was to make the correct binary choice (defend the weakest gate at King’s Landing). He still eventually lost the battle, but was saved by the combined forces of the Lannisters and Tyrells.
Everything else has been of a political or technological nature:
- Helping Jon Snow’s and gaining his trust as a member of the broken, bastards and cripples
- Getting the hill people to help him instead of kill him by promising them the Vale
- Determining that Janos Slynt had to be eliminated
- Figuring out who was Cersei’s mole in the small council
- Unraveling the secret of wild fire was more about his ability to ferret out information
- Getting the slaver to take him along with Jorah and not kill him immediately for his dwarf penis
- Forestalling the Son of the Harpy by making a deal with the powers of Astapor and Yunkai
- Getting Daenerys to listen to Jon, and vice versa
- (Book) Getting Aegon Targaryen to go immediately to Westeros instead of trying to woo Daenerys in Mereen
Tyrion is a genius at political maneuvering, reading people and giving us the wittiest insults in Westeros, but he’s never been a good military commander.
However, his plans have been the work of either an idiot or a traitor.