A pyramid scheme makes money by taking finances from the bottom and putting them into the pockets above them. It doesn't generate revenue on its own. This is why they inevitably collapse.
steembasic income rewards STEEM through upvoting. STEEM that is given out is immediately given back, in portions, over time. I think the number is 6 months that you break even, assuming you continue to post on the STEEM blockchain.
The point is, that SBI guarantees revenue to those who 'invested'. The creation of more STEEM through upvoting content is a form of revenue generation ('mining' the STEEM blockchain). For this reason it can't be called a pyramid scheme IMO.
The creator could of course power down and run off with the STEEM, and then people lose their guaranteed SBI, and assuming that everyone did not get 100% of the STEEM they invested back, then it could be called scammy. But they haven't done then, and me personally I've made all the STEEM I put in, and then some.
@josephsavage thanks! and I'll try to remember putting some more SBI to folks next rewards payout.