ok, so i have noticed that characters like Zero,Dante,Magneto,Ammy,Joe and Doom can get extremely long ground and air chains but characters like Trish and Thor and Iron Man in my experiences cannot get combos nearly as long.
Like with trish when i used to play her i noticed she struggles to land anything after “ground chain S air chain dive kick ground chain S” the opponent will be able to tech abnormally quick. So while im pretty sure the different moves have different deterioration “points” but do all characters have the same amount of “points”?
I’m not sure but certain characters have moves that aren’t subject to hit stun deterioration such as Ammy that you mentioned. Zero and Magneto both use a LOT of H’s which have a much lower hitstun than say … Trish’s combo. Doom just gets a ton of cancels off his flight=>adf because his normal aerial mid already starts with a good chunk of hitstun tacked on I’m not sure if it helped your answer any.
theres some super complex ass formula that capcom uses to decide hitstun deterioration. there are lots of factors that ive found but here are some that ive found to “mostly” be true:
repeated moves cause it to scale faster.
light attacks cause it to scale faster.
certain special moves cause it to scale faster.
TAC and launchers slightly reset hitstun scaling… how much seems to be a crapshoot from combo to combo.
i “think” doing certain moves in certain orders cause it to speed up and slow down.
certain multi hit moves dont cause hitstun scaling “or do VERY little” until the multihit move has completed (probably to keep characters from popping out of something like a hit tatsu in the middle of its animation… pre patch 2.0 ammys F+H series is a good example as that move was unaffected by hit stun scaling, but still added to hitstun scaling after it was done.
anywho we will probably never know all the rules of hitstun scaling cause there are probably all kinds of “special” moves that break the generic rules, setup by capcom, on purpose.
for instance trishs divekick may give an inordinate amount of hitstun scaling… or it might only give alot of hitstun scaling when done from a superjump… or maybe theres some completely different answer for why that specific combo ramps up the scaling so fast…
omit the 2 L’s in the combo and it may be alot easier to do and you might be able to tack some other stuff at the end like another launcher… maybe.