If you literally could not tell the difference, then something may have been wrong with the demo. It is true you do need the brightness turned up, since you can't get the range if you cut the top end down too far in the first place, and I've seen it said you really can only get it in a dark room because of that.
If that makes you less interested in getting HDR because you don't always watch TV in a dark room, well... yeah, it's definitely a more niche feature.
However, IMHO the more interesting thing about the HDR standards is the improved color gamut. That is quite noticeable when you get content that uses it properly, but there's precious little of it right now. However, I do occasionally commit videophile sin and turn on my TV's "fake up a guess about how the color gamut might look" mode even though my media isn't technically mastered in that, and there are some things that it does make beautiful, even if it is technically inaccurate. Inside Out in particular is jaw-dropping on my TV in Fake-o-HDR mode. (Which isn't entirely implausible, as I understand it the original movie is in an expanded gamut, but there's no Bluray that has the expanded gamut version AFAIK.)
If that makes you less interested in getting HDR because you don't always watch TV in a dark room, well... yeah, it's definitely a more niche feature.
However, IMHO the more interesting thing about the HDR standards is the improved color gamut. That is quite noticeable when you get content that uses it properly, but there's precious little of it right now. However, I do occasionally commit videophile sin and turn on my TV's "fake up a guess about how the color gamut might look" mode even though my media isn't technically mastered in that, and there are some things that it does make beautiful, even if it is technically inaccurate. Inside Out in particular is jaw-dropping on my TV in Fake-o-HDR mode. (Which isn't entirely implausible, as I understand it the original movie is in an expanded gamut, but there's no Bluray that has the expanded gamut version AFAIK.)