d4 has its uses for defensive spacing and to bypass high projectiles inside jump distance where you can't IaTu.
Simply think if someone like Sonya tries a Ring from jump distance , you can't IaTu on reaction , you can't jump on reaction but you can dash into a d4 and get the frame advantage , now when you go on hit with d4 your offensive followup depends at what distance you are left.
Max range d4 doesn't have guaranteed followups other than linking a flamethrower wich is often unpunishable by characters that don't have fast advancing special , however you can start the guessing game and it's in your favour , f2 catches jumps ( wich can turn into combos ) , dash b3 / b34 ( can be jumped if they commit to it tho ) , b1 , dash 1 to check them , remember to mix this up a lot and you may even sneak in with a throw.
Close range d4 has many guaranteed followups , dash 122 , b34 , f2 and when you conditioned them enough you can throw or even u34.
Now it's clear that you won't always go on hit with d4 while spacing so you gotta be aware of the guessing game after a blocked d4 , you're at even frames and you have some pushback so if you jump back he can't d4 , 21 , 22 because you're out of range and he has to dash in to make them connect so he's left with reading your backjump and slide it , if you do d3 and he dashes in you will outspeed d4 / d3 / 21 / 22 and get frame advantage ( +2 on 21 / 22 and +8/9 on d4 / d3 ) to start your offensive , also if you read a dash in 21 / 22 after a blocked d4 you could 12b1 and hitconfirm into a combo ( this is purely a guess but at the same time sub can't do much other than d4 / d3 again or try to space his 22 to make your 12 /11 whiff ).
After a blocked EX Tu against Sub Zero you can limit his options with a lowpoke , STH you say d1 is good after it but d3 has a better guessing game if it hits , first off doing d1 after EX Tu will not outspeed d4 / d3 and they can crossjump you to continue pressure , now since d1 ( as every lowpoke ) lowers Sektors hurtbox it will go under 21 / 22 / throw , but the thing about d1 is that even on hit is -7 so you can't get your offence started at best you can go back to your spacing game , d3 on the other hand leaves you at advantage while going under everything d1 does , also d3 on block is -8 but has very little blockstun so you may take advantage off the opponent not reacting fast enough and go back to your spacing ( and don't forget the 6 frame launcher ) , tl
r sub hasn't got any fast special mid to close your options and combo off it after a blocked EX Tu.
And as everyone says stay patient when you're in the corner and make him sweat getting you there , midscreen sektor wins over sub.
