You have read a lot around BLF Flintrock, way back into the match days
clemence has had boards made for the new Nichia leds that have a direct connection to the core at the cathode side (where the most heat is produced), and in fact I will be getting some leds to test on his boards. It gives me the opportunity to see how much that differs from my non-DTP boards.
As discussed in the OP, what may be a big factor in how well a non-DTP board sheds the heat is the quality of the dielectric layer. In my 6xXM board test I may have struck a non-DTP board with a good layer while other non-DTP boards may have worse heat-shedding properties.
They do work and I tested that they work well (though not as good as the VirEnce board), but it requires scraping off some solder mask to widen the solder pads.
A DTP board will always heatsink better than the board from the OP, but only work with leds that have a (neutral) central solder pad.
The OP board fits all leds that have just two solder pads for cathod and anode without central solder pad. And there is not so many leds that fit it that are interesting in flashlights, it is an obscure board!: almost all midpower leds have the two pads but are too dim for flashlights, a series of Nichia UV leds fits this board, Luxeon Z fits it, and with some scraping the Nichia 144A series fits it.
Maybe it’s not (only) the dielectric layer that is better than usual, but it may well be (judging by the picture) that the copper layer on top is thicker than usual.
I was thinking XQ-E, but they’re probably too small for that.