Funny story - I was attempting stage 9 on hard and found it nearly impossible, and on my third try I just decided to let it play out when I was losing pretty bad. I lost all my units except for both planes, and had to sacrifice one to destroy the commando that was about to take my only factory (and had already taken my ground control). However, I managed to slip by the huge flak tank clump and get into the center of the map. At this point the AI apparently forgot how to make units, so the one rocket truck he had chased me around unsuccessfully. I saved up until I had over $5000 and made an army of ships (mostly battlecruisers), which I slowly pulled out of my only factory. I then proceeded to wipe out the AI army, because the AI still wasn't producing units.
TL;DR Stage 9 hard mode is absurdly difficult but it balances out by the AI breaking after destroying almost all your units. Survived with one plane, then made a ship army and won.
 "Arcuz - Behind the Dark"){kind=icon}
 "Battalion: Nemesis"){kind=icon}