Strictly multiplying by 8 isn't really a good comparison, as the cost of supporting such a network in India isn't going to cost 1/8th as much as the US. I'm sure there's a lot of room for the US cellular carriers to be more efficient.
In reality though, I think many US users here probably get the majority of their bandwidth over WiFi and do not really use that much LTE data. But, if I wanted to replace my $70/month cable Internet with just a Mint subscription, i.e. the $25/month plus 2x $20 refills, that would buy 18 GB/month of LTE.
I do, however, have truly unlimited, which means I can tether without hesitation. T-Mobile does have unlimited plans at $35/line a month for 55 or older, but that is still twice the $18/month price.
As the sibling post states, there are competitive plans like Mint, or FreedomPop, which offer extremely cheap plans, but nowhere near 1.5GiB of data a day. So I guess we are much further away than I thought we were.