The reason why you will hear it said that the variance in plo is a lot higher than Holdem is due to the fact that the starting hand equities run so close together. This is why people advise a larger bankroll. But I think this only matters more when very short stacked hu.
In Holdem getting your AA in preflop you will be 80% or better to win the pot basically if out get called, but you rarely will be anywhere near this good getting it in pre in PLO (even with AAKQ type hands). But if you have time to play a bit of proper poker correctly you can have massive +EV against bad opponents post flop. Their are many opportunities to steal\bluff well, free roll pots with outs against people who have the same current nut hand as you and sometimes you even get a lot of people calling you when they are drawing dead. This is never usually happening in Holdem where for example your top pair top kicker can be called by top pair lower kicker etc and they still have like 12% equity.

I find when playing the NL omaha hi lo hypers the variance is massive though and you end up splitting so many pots where you had a very good chance to scoop e.g if you low gets counterfeited. But you can make up for it by being able to play a lot
of volume in a short time.