Your experience is why I'm curious about that. The M6 is really just a new body. They did little to no development on the driver. The shared drivers is a big part of why so many chinese lights are as cheap as they are. Also, the lens doesn't even have an antireflective coating and the box is plain.
In your example of the TN30, as you said, manufacturing is not going to have a huge difference in those costs. Where Supbeam Acebeam benefits is that it can reuse their design and drivers in the TN30, TN31, TN32, TN35, K40, K40M, K50. The X40 and X60 and X60M drivers may share core driver technology too. We also see better prices from Acebeam because they're willing to work closely with enthusiasts to give us huge savings from normal retail pricing, which I can't imagine Nitecore doing at all.
Then there's brand value. They make a wide range of lights to suit many needs, which means there's many types of customers that can recommend their products, including vapers that would only use their chargers and batteries. Nitecore actually has a relationship with their vendors. Their official vendors provide warranty support, and either those vendors or Nitecore sends their gear out for testing. Maybe not the friendliest relationship, but it's better than Supfire. From what others have posted before in group buys, dealing with Supfire is a lottery, and not a good one. It's like they're all bipolar. There's no warranty to speak of, and I don't believe they've sent out anything for review. A strong brand is worth paying more for, and people will pay that for Nitecore, but the Supfire brand is worth very little. If Supfire went out of business before the end of the year, it wouldn't surprise me at all, but I fully expect Nitecore to be around in three years.
Whether they're overpriced really depends on how much Nitecore is making, but I doubt that's what you really meant. You probably meant the value to people like you. If what you care about if lumens, lux and nice mode spacing, then no, it's not worth it. If you a light that is nice to show off because it has a few features that other lights don't, and possibly higher quality, then it might be worth it.
Would I buy the TM26? Not a chance. Not even at $100 unless my plan was to sell it. That's not because the light doesn't have value, but because what makes that light special isn't valuable to me. I don't care about the screen, or the warranty, brand equity, better surface finish or fancy box.
I definitely wouldn't buy the M6 at $100 either. It's an unfinished light. To be worth $100 it needs new emitters, mcpcbs, driver, spring wire mods, and a lens with antireflective coating....and a box with fancy printing if I was going to sell it to regular people.