Thanks for the responses. I’ve now found a new old stock Stanley Jennings bit on eBay. The difference is night and day. The Stanley bit has a slightly finer thread and a full snail with no flats. It pulls itself into the wood no problem at all. (Well, it requires a good bit of arm strength 😂)
What a shame. Fisch seem to be the only company making an attempt say these bits but sounds like the larger ones are just no good for hardwoods.