I wouldn’t say that learning cr.HP xx HK Lightning Legs is a waste of time. Chun has a bunch of offensive options from it, plus it costs no meter (in fact you gain almost an entire EX bar from it), it does a lot of damage, and a lot of stun.
If you are consistent with the link into sweep, it also gives you an untechable knockdown, which is always good.
If you’re not confident about the link into sweep, you can do cr.HP xx HK Legs [MK Legs] > cr.LP > st.LP > f.st.HP. This is an easy, easy, easy link getting the jab off cr.HP xx Lighting Legs since it leaves you at +7, and after that you just autopilot into Chun’s meterless BnB.
You can also link EX Legs straight off the frame advantage and have it combo, then follow up with U2. If not, linking cr.LK is easy and then cancelling into EX Legs should be cake too.
My favorite one so far is:
[In the corner]
cr.HP xx HK Legs [MK Legs] > cr.HP xx HK Legs [MK Legs] > cr.HP xx EX Kikoken xx Level 2 Focus Attack [Crumple] xx Dash Forward > [Wait] df+LK > Headstomps