Vanguard's Total Bond Market Index Fund (VBMFX) may be larger than PIMCO's Total Return Fund (PTTRX), but it doesn't necessarily mean the passive investment strategy has triumphed over actively managed funds. That's according to Michael Herbst, director of manager research for fixed income of Morningstar. In an interview with TheStreet, Herbst said some investors may return to a more active investing strategy once markets become for volatile. In PIMCO's case, he says the fund firm has received a lot of attention since losing assets following the departure of Bill Gross, but less attention has been paid on the fact that those outflows haven't had a big impact on performance. He says the fund continues to perform well and that PIMCO has a talented investment team even without Gross.