Unsure if this was intended as some arrows only show the secondary particles during crit, as if they were intended to replace the regular particles rather than emit both.

It's impossible to replace the original vanilla particles unfortunately. At least in 1.16.5.
Would love to, if it was possible!

I see, it seems Mojang only allows an override to a method for particle emission in AbstractFireballEntities. Thanks Mojang.

If it were possible, it would have been done like this

the below is example code from my gun mod, all you need is that method override