Thrawns not so great, c'mon, Ren coulda thought up Mole Miners...
The whole shooting through Shields idea, overblown, why make it look like you can shoot through shields for a single engagement, when youve already got ships below the shields. I think the phsycological impact of the ships under the shields strikes more of a blow than looking like you can shoot through them.
No. Your theory would have worked for one engagement, and would have won him the one planet. And you probably would have just used the stealth ships to blow up the shields anyway.
Thrawn's theory won him a planet, with its defences intact, and it frightened other planets into surrendering without a fight. Even without being repeated, the "superweapon" won battles.
To make your theory work, you'd have to infiltrate enemy worlds every time you had an egagement - and the enemy would grow wise pretty quick.
Not to mention that the planetary guns would probably blow your ships clean out of space as soon as they saw them...