B12 is slower and less far reaching than in Piercing.
F23, may be able to do this but remember, you're -7 after it, and not -4 or -5, so you can get punished with 5 or 6 frame normals, and up to 7 frame specials.
As far as the high pounce question, hopefully someone can answer that. I'm not too familiar with Ravenous, sorry.
Some stuff about the F234 string, B12 theory and Ravenous:
F23 has so much pushback that not even Kung Lao ex spin punishes it, nor does reptile ex dash. Only Reptile ex slide works, and that is very little damage for one bar. I.e: you are
not going to get punished after F23. F234 is easily punishable by most, but F23 > (exroll_3) gives her a mixup opportunity. Sadly high pounce wont work after a blocked F23 so in order to threaten with an overhead you need the meter. Anyway, as long as you have meter it is scary for the opponent to press anything after F23, which will make the hesitate.
In fact Id argue that
B12 leaves you in a worse situation on block than F23. You are forced to respect their options nonetheless, but after B12 you are left much closer to the enemy.
Mileena has terrible frames up close so outside of oki situations, even if she had a move that was +1 on block she'd still struggle to check people due to her lack of a good quick mid that hits low profilers, her 1 and 2 both being slow and her d1 being terrible. She'd have no way to make people respect her in that situation except for ex roll, which is risky to say the least.
She is not a frame trap character, and that is fine, she has other stuff. I do however think that people overestimate the frames for b12 in Piercing for these reasons. Being slightly minus with Mileena and close up is a really bad place to be in. It's still an excellent poke/whiff punisher, but rather than talking about how minus something is, in Mileena's case pushback is more important (as long as the attack is safe that is).
For Ravenous the pounces do help her after F12b4 on block in oki situations such as after 21u4 though, since F12b4 xx low pounce is safe vs most of the cast and thus makes it safer to commit on the low after F12. F12b4 xx high pounce works too but it's pretty gimmicky since the enemy is probably going to do a high/mid after the F12b4 on block (-6) since they can force a mixup, and thus high pounce wont hit.
Sadly she is only slightly plus on hit after either high pounce or low pounce hit, and cannot force a mixup, very much like her post-throw situation.
