What wing chun principle, concept, tactic or strategy comes to mind that you would considered flawed when applied to groundfighting?
If you look hard enough for WC principles in the tactics used by skilled groundfighters, you can probably find them, but not everywhere.

You could, with about the same ease and validity, look at a skilled standup fight and point to where one or other of the practitioners used sound BJJ principles (if all you do is WC, how would you know?)

The fact remains that, no matter how strong one's theoretical base may be, that if he doesn't spend significant time sparring with and learning from good groundfighters and learning how THEY apply sound groundfighting principles, you are not going to have the experience base to apply those principles, and counter the more experienced fighter's applications of them, and are going to get comprehensively beaten when the fight hits the floor.

You want to beat BJJer's? Sambists, MMAers? You need to learn what they know, as well as what your WC ancestors know. One way or another, you need to learn BJJ to hold your own against BJJ - same applies to any other discipline.

The WC strategies aren't necessarily flawed ... it is just there are some areas of fighting for which they have no application at all. Pin escapes are the most obvious example.

Props to the HFY successes, but ...

Fighters from my organisation have won fights at entry and intermediate levels in boxing, kickboxing, MMA, and BJJ events over several years. We won or placed in every division we entered in the Tasmanian BJJ championships in 2004. This is just part of testing your art and moving to another level ... there didn't seem to be the need to post blow by blow details of our successes or imply that we were somehow bringing WC out of the MMA wilderness all on our own.

At the BJJ and MMA club I go to, people have ring fights regularly, and win a fair number. These people get a round of applause at training, and a mention in the club newsletter, but if every MMA club did this for every event MA forums would be filled to overflowing with these results and nothing else.

When one of ours, or yours, win an elite level event, THEN we'll shout it out.

We crosstrain, and IMO so should you.