There are a couple of things that make the TH400 "better" especially for drag racing.

When modified with a manual valve body you don't have the shift overlap problems inherent with the Torqueflite design, in the TH400 you just add clutches to upshift...no release/apply overlap.

Also, the "wrap around" case design of the Th400 is stronger than the open bottom design of the TF...less case flex.

As far as the "time bomb" argument...ALL automatic transmissions can explode; that's why NHRA requires diapers/shields on all of them.