A topic for debate, certainly, e.g. here. Perhaps not worth the risk if you're unsure whether your boots' stitching is synthetic, particularly with so many more advanced products now available.
I also found quite a few threads from that time (2007) and before. Dubbin comes from the old verb dub meaning to dress leather by rubbing. Thus anything used for this purpose was called dubbin and the ingredients of dubbin are not standard. In the good old days (when I was a lad) it was basically lard or tallow but the modern stuff is very different even though it has retained the name to indicate its purpose. Cheery Blossom, Kiwi, Mountain Warehouse, Dr Marten to name but 4 sell their own brand of dubbin. I would be very surprised if any of it rotted stitching.
I can only find old threads discussing the idea that it might happen and so far I have not found anyone reporting it actually has happened. As a boy I used to put dubbin on my football boots and even then, when the stitching may well have been cotton, the stitching stayed solid.
Equally, I have had boots where the stitching has given out and, had they been treated with dubbin, perhaps I would have blamed that but I haven't used it for over 50 years.