During really odd years (2007 was one) I had some MF distributed 20 -25% as the market slowed down. No this was not an index fund, but this is a reaction after some number of good years and people start pulling out their funds. But I did not pull mine out at that time.Yeah, I think you've got it.
My point is that with MF's I get get taxable CG distributions every year I have to pay taxes on. With ETF's the CG's accumulate and will be adjusted to zero at my death.
As more indexers retire and take more $ for retirement, we may see higher taxable distributions due to retirees taking larger RMDs. I would think the index funds internally have investments with high gains.