Firstly, I would say that its really very possible that there are a whole bank of individuals out there who can legitimately fight using all manner of different things but whom simply don't care about the lime light and have no desire to teach. I have met a few people like this. People who were on par with famous teachers, but were content just to train and train. IMO they are likely to surpass the famous teachers because they dont have the burden of teaching.. they have more time to train! But you will never hear about them, or know they exist. So the absence of a 'successor' may well not be indicative of the training methods validity.
So for example, I would have absolutely no problem (as a Chen stylist by preference) walking into a good Wu style school and going through the Wu style program, but if there was a Kungfu school that taught the 24, 48, and combined 56 or something, I would not really want to go to that school (even if nothing else was in the area).
Ironically, I have heard from several teachers with very complete lineages of Yang Style, who could fight, that they teach the 24 form as a primary initial form before being bogged down in the 108. Even though it was never actually part of their traditional syllabus. So i wouldn't assume that the 24 form = Wushu performance = crappy. I think its a common 'add on' for a lot of Taiji schools.
IMO, for fighting, the form itself isn't particularly relevant, neither is the purity of the lineage. The meat of the matter is in the method of training the body and the approach to partner work. Many Taiji schools, even ones with very good lineages, fall down on the second part of that equation IME.
thanks.