You're incorrect....if you buy 10k worth of GC at the mall, you will spend $79 + about $7 in MO fees at WM to clear them out. For that effort and expense you get EITHER $201.60 OR about 10k SPG points. Your logical flaw is to count the cost in the cashback scenario but ignore it with the points. I bought $201 cashfor $86, you bought 10k SPG points for $86. So now we compare the values of what we got out of this activity....which is $201 vs 10K pts.
Furthermore, if you're a moderately well to do middle class person, like many in this community, you probably pay around 30-40% marginal tax rate. This effectively means that any CB profit is multiplied by around 1.5x when compared to just working more at your job/business. So my $110 CB profit is really more like ~$160.
I'm sure the are some examples here and there, where you can get good value out of SPG points for somewhere you really need to go, and where you have no choice but to pay through the nose, and a Marriot/Spg hotel saves the day. I don't travel to overpriced cities nor do I think $600+ a night is worth it or justifiable. I can always find an airbnb or much cheaper hotel that works just fine. Also, if low tier hotels were all over the place in National Parks around US, I'll be all about hotel card MS....but I just did a road trip around Arizona and UTah and not once encountered anything from a chain besides Best Western or similar....and they were all under $100 anyway. I would probably find more value in Miles transfer personally, but I have more miles than I can use now so it's not a priority.