I've managed to beat the game on Hard several times. The trick is you have to constantly keep pressure on the enemy, don't let them build up a full army. Send in a unit to draw their troops out, then retreat so their next units don't join the fight. If they get a large number of guys at your base, you're dead.
I've finally made Hellstone lv.100 my most efficient. I am now done with this game.
Final Stats:
Good Hyper Pick +29
P: 14,156.58b
Q: 1754.95%
Blacksmith:
Base Power: 806.66b
Average quality: 130%
Expertise: Lv 10
Efficiency: 30%
Gem Waster: 133 gems
Manual Click Power: 5110%
Auto Click Power: 2858%
Auto Click Rate: 13.51 clicks per second
Idle Power: 54%
Stats Vs. Hellstone lv 100
Damage per Click: 35.87qt
Auto damage per second: 205.73qt
Auto gold per second: 22.15o