As someone who came to bikepacking after mountain biking for many years I can say that I shared your skepticism at first. However, after getting several bikepacking trips under my belt now I can say that I've converted to a full-blown bikepacking advocate!
I will say, though, that it definitely requires a different mindset than mountain biking. If you're solely looking for the mountain bike 'flow' you are correct that you will not enjoy all the additional weight. However, with the right gear (again you are correct that it can be expensive), you can get most of that weight centered on your bike and have a surprisingly low impact on your riding.
I'm including some photos of a single overnight bikepacking trip that I did over Resurrection Pass on the Kenai Pennisula last year. We managed to cover 40 miles in two days, which was only possible because we were on bikes. One of the biggest appeals of bikepacking is being able to move relatively quickly through the landscape while still very much feeling like you're a part of it.