Corner grab into oki, generally you just have to do 5D if you want 5D oki. if you want jD, you can do 2A 5C 2C 214B j2A jD
With distance however, you can do j214B (5B/2B jC j214B, like you posted) ender into 5D oki (react and punish dodge with 5A if you dont do it tightly enough) if you WANT 5d oki and are willing to spend 25 meter for it, grab 2A 5C TK j214AB works (you can also do 1 more lion rep into 5AAA ender if you want damage off of this).
If you set up oki with jD and land another grab (has to be staggered, for example like...j2A jD meaty 5A 2A grab), the way izanagi forces himself into the corner gives you more distance for the grab letting you actually get away with grab 5C 2C backdash sweep 5D.
generally, most dp's can be baited by crossing up. i really dont have too many strategies, aside from good spacing + 2C backdash beating some counters (chie comes to mind)
im sure someone posted it before, theres an option select you can do to deal with supers after mitsuru's DP
uhhh, as far as beating dp's goes, safe jumps safe jumps safe jumps. you get safe jumps off j214B (though you can just go for 5D oki lol) and 214C which is how i would end /all/ of my midscreen strings.
tl;dr good spacing, stagger your normals, safe jumps. 2C backdash is a good tool due to its good range and short burst of invin from the backdash which dodges some counters after activating them, but thats about it. There are some option select punishes for DP's to deal with super cancel however.