The amount of inflation generated by HBD interest is very small compared to other sources of inflation in Hive. There's a couple of reasons for that: 1) HBD total supply is effectively limited to 10% of Hive marketcap and 2) most of that HBD is held on exchanges and in the DHF (i.e. not in savings account where it can receive interest payments).
RE: HBD: The "Safe" Stablecoin?