Fair enough. I'm also not a geoscientist, and to clarify I didn't mean to imply any specific statistical effect there. It seems entirely reasonable to me that a series of EQs might tend to increase in intensity.

In reality I think (layman's impression) that there's rough (post hoc) evidence for both things. Foreshocks followed by noticably larger EQs as well as trains of progressively smaller EQs.

Precisely, and the 'myth' is worded in such a way that the effect of stress relieving pre-quakes is set to a big fat zero and that seems to be a thing more related to the composition of what is underground than the fact that it does not happen at all, and if it happens at what magnitude you would expect the effect to show up.

To me a myth is something that isn't true at all, not something that we do not have data on to be able to rule it out completely or that may be an influence just not a capital one. I think the most generous reading of the 'myth' claim would be that the energy available in the smaller quakes is too low to have a meaningful effect on releasing energy from a larger quake and I'll buy that. But at the same time an absence of such fore-shocks in an area where earthquakes are known to happen indicates that stress may be been building up over a longer time and that stress would be released in the next bigger quake if and when it happens.

This too may not be a big enough difference due to the immense increase in energy present in larger events (the scale is logarithmic). But its effect is quite probably still non-zero and for it to be a myth it would have to be zero.

Myth = the sun rotates around the earth

Myth = unicorns exist

Myth = the earth is 6000 years old

Those are directly falsifiable, and we know all of these to be categorical falsehoods.

Smaller earthquakes can - depending on local crust composition and other environmental factors - affect the amount of energy released in a larger one following, is not necessarily a significant effect (though even this would be tricky to establish) but I find it hard to believe they are completely unrelated though the effect may not be large.

Insignificant effect != Myth