Just check out some high level King play, like the Answer's at NEC or Bala's in the arcade version, and you'll see what I mean about her close range game. Its what makes her dangerous.
Its all about mixing it up, if you do the same df+D into fireball all day of course you will get punished. Its worth mentioning that the opponent does need meter to punish.
Actually, because st.B, df+D xx Venom Strike usually produces a Trap Shot accidentally, most players delay the df+D xx Venom Strike so its timed as a late cancel. This gives the player enough time to return the stick to neutral and perform the Venom Strike correctly. The magic of this is that late cancelling the df+D doesn't affect whether the Venom Strike combos or not, because the slide itself has such great hit-stun.
There is a gap between the slide and the late cancel Venom Strike. If you perform an invincible move during this time, you beat King's Venom Strike (1 frame throws can work too). If the King DOES NOT like to late cancel during blockstrings and you attempt a reversal, nothing will come out because it is a TRUE blockstring. Essentially, it's like a ghetto option select - it carries no real risk for the defender of King's pressure. Reward if it's late cancelled, continued block if its immediately cancelled.
King's post Venom Strike (on block) pressure is fairly weak as well. st.C and st.D are both jump checks, and completely whiff on crouchers. Not to mention she is not at frame advantage after one of her blockstrings. With this in mind, most character's cr.Bs either beat King's next move or avoid her jump checks and punish her. Before I forget, she's absolutely horrid on defense as well. EX Trap Shot is the only tool that can save her from overwhelming pressure.
edit: But I still think she's high tier. Amazing zoning, great mobility, annoying pressure, one of the best fireballs, great metered moves, good corner game, good meterless anti-air, and Slide!