You are correct that the MSCI world momentum ETF has outperformed the total market ETF over its lifetime, which is since about 2021. Almost all of that outperformance was in 2024, which was an "up" year. I would expect momentum to do well in up years and less well in down years. Let's see how it does over a full market cycle.
I agree that these factor ETFs mainly generate an extra return for the banks, as the generated fees are much higher.
But the MSCI World Momentum Index seems to be nicely outperforming the MSCI World Index for a long period of time, that's why I favor it.
You are correct that the MSCI world momentum ETF has outperformed the total market ETF over its lifetime, which is since about 2021. Almost all of that outperformance was in 2024, which was an "up" year. I would expect momentum to do well in up years and less well in down years. Let's see how it does over a full market cycle.