Your standard acoustic guitar is really mostly air,

You've clearly never played an Eko. I passed mine on to my son, and I sit down whenever I play it.

I think I'd find that belly bag arrangement a bit tricky, but if it works for you, it works for you. A lot of guitar straps are a bit on the thin side, and if that's the case with yours, it might be worth experimenting with a broader one that spread out the weight more.