It is as the part I bolded, only MP DP has 5 frames (they stealthily introduced this in AE I guess, because while I can’t remember it in the change notes, but I’m sure it was 4 frames in Super - I remember strong players like Valle or Umehara not antiairing with the absolute ease a 5f MP DP allows, and you confirmed it with the hitbox data), so one might go for it when he doesn’t want to risk a DP with 1) less invincibility 2) no fadc’ing out if mistimed.
HP DP had only 2 frame (down from 4) of invincibility in Super and AE, it became essentially useless: you don’t antiair with it, you usually end combos with Tatsu, you combo into ultra with LP DP since it adds +50 stun. Now it’s back to 4 frame inv. like vanilla and they give him a slight boost in damage and different properties (not fadc’able, 1 hit only) in order to make the player choose between his DPs.
It’s not bad actually: not a strong buff, but it adds a bit of damage and diversifies the gameplay. In Vanilla MP DP was Useless. In Super and AE, HP DP had no active incinbility and was less usesed. In v2012 I still see MP DP being the most used (fadcable, best invincibility, damage still solid), but stronger players will net +30 damage when antiairing with fierce and don’t feel/need to ultra.
It’s not that different for Akuma. Only, we got a horrendous LP DP, and have to choose between more invincibility (HP DP) at the cost of less damage (80/80 most times) and better damage (MP DP) but less invincibility.
tl;dr version
Vanilla
MP DP > 4f inv, 130 damage (1 hit)
HP DP > 4f inv, 160 damage (1 hit)
Super
MP DP > 4f inv, 130 damage (2 hit)
HP DP > 2f inv, 150 damage (2 hit)
AE
MP DP > 5f inv, 130 damage (2 hit)
HP DP > 2f inv, 150 damage (2 hit)
v2012
MP DP > 5f inv, 130 damage (2 hit)
HP DP > 4f inv, 160 damage (1 hit)