If the first TK badland whiffs or only hit once against characters like May, you're most likely inputting the TK BL too early or doing a ground badland instead. The window for inputting the first TK BL against light characters such as May is larger than it looks, so you should delay the tk BL a bit. It's easier against Bridget and Baiken too.
I don't think anyone took the time to list the best badland loop for each character, so I'm going to list the ones I use. In my opinion these 3 options are the most practical:
1- BL > [tk BL] * N
It does the best damage against May, Bridget, Jam, Millia, I-no and Dizzy. It's also the practical choice for Axl, Zappa and Eddie, though there are variants that do more damage. You should be able to get 6 reps against the lightest characters, 5 for I-no Millia and Dizzy, 4 for everyone else. You can go for a 7th rep against the lightest characters, but at the cost of the knockdown, so I don't recommend it.
2- BL > tk BL > 5HS > BL > tk BL
Works pretty much all the time against Slayer, Chipp, Johnny, ABA, Ky, Robo-Ky, Testament, Faust and Eddie. It's spacing specific though, if unsure go for variant number 1.
3- BL > tk BL > dash > 6K > 5HS > BL > tk BL
Works best against Sol, Order Sol, Anji and Venom. Also works sometimes against Zappa and Axl. Once again it's spacing specific.
These 3 variants cover every character but Potemkin, against which you have the brain dead easy [5HS > BL] * N loop. Note also that there are almost no viable setup
for badland loops against Dizzy.
The main setups for badland loops are:
ground throw:
throw > 6K > BL > tk BL > ...
against faust and baiken:
throw > dash > 6K > BL > tk BL > ...
corner 6P/2K/2D:
(6P/2K > 5S) > 2D > HS Exebast > 6K > BL > tk BL > ...
HS Exebeast counter hit:
HS Exebeast CH > dash if necessary > 6K > BL > tk BL > ...
after midscreen 1-hit BL setup:
1-hit BL > land > 5HS > BL > tk BL > ...
midscreen up close 2D (after a blocked S Exebeast FRC for instance):
2D > HS Exebeast > 6K > BL > tk BL > ...
midscreen 6P/2K at a very specific range only against very light characters:
(6P/2K) > 5S > 5S > 2D > BL > tk BL
Basically the 2D has to hit the opponent as far as possible for this to work. Omit the
second 5S if far enough.
Badland loops look cool, hit hard and give a lot of meter, but they are really difficult to execute properly and do not push the opponent toward the corner. Also, no meter gain after a Beast FRC or Gravedigger, which makes them only really useful in specific tensionless setups. 1-hit BL are much more important to master in my opinion.
I hope this helps . I can do a similar post for 1-hit badlands if anyone is interested.