There are way more Davids up against the ETF Goliaths, and it’s starting to take a toll. The combined share of ETF inflows for the three largest ETF issuers was around 80% roughly six years ago, but now sits at just 55%, according to recent data shared by Bloomberg Intelligence. The chipping away of BlackRock, Vanguard and State Street’s dominance is in part due to the boom in new ETF issuers and funds. Last year, the US saw 1,000-plus ETF laun…