OK, The problem with dropkick aint so much its damage. Its the insanely quick and invincible startup of the level 4 kick, combined with the fact that two kicks may be charged concurrently, combined with the high damage on each.
Crazy idea: Up the L4's damage to 325, but make it an EX and require BOTH buttons be charged the full 16 sec. Make the level 3 the maximum for 1 button, and improve the speed and recovery on the level 2 and 3. Damage would become 100/125/150/325. Releasing one at a time would still allow 2 powerful kicks, together would yield the EX kick.
That neatly closes the BS 100% combo on 3 stocks and 1 DC loophole without nerfing the kick into the ground. The EX version is GDLK (and the time and meter cost combined more than justify the damage, speed, and invul), and you still have some pretty buff combo opportunities out of it, including probably 100%s via NM. Raiden, like the rest of the cast, would still need 4-5 stocks to break 85-90%.