I just tried using a stick I bought a long time ago but neglected using because of giving up but recently picked up again because this thread has sparked my interest in trying again. And I just found a neat tip for anyone having trouble with special inputs.
In the case below, I was trying to input a 214B but just couldn't get it to come out right and almost always getting 2B instead. I turned input display on and here's what I got:
In the case on the left, it shows that I pressed the B button a teeny weeny bit too early, during when I input the 1 direction, which resulted in the 4 direction in the 214 to not be read. This causes the game to read the input as 21B, not a complete 214B, and a 21B results in just 2B, thus F-ing up everything up.
To solve this, I delayed my B button press a teeny weeny bit which resulted in my button press to be right when (or after) I input 4, resulting in a complete 214B, as shown in the case on the right.
Hope this helps someone.