The most annoying thing in that regard happened to me when I added psionic to my erudite brainslug species by using a template from a psionic AI empire in one game and all existing leaders lost erudite and never got psionic.
Now I only go for psionic/cyborg/brainslug leaders if I chose psionic ascension if the option is there(I always get brainslugs at least in huge galaxies.)
That only works for existing leaders though because new leaders can only spawn with 3 traits and one of those is always a leader class specific trait like genius and they spawn without brain slug.
If you stack some lifespan options one leader lifespan is usually enough although I tend to move the crisis forward.
In most games I just use what I get but I just can't resist donating a planet to a DA if one is in the game.
hmmm... what about latent psionic and erudite ? Start with an erudite leader that later gets found out to be psionic. I wonder if that coud work.
Some people claim that you can get erudite and psionic on existing leaders if you create templates with one of each and mod that species from one template to another and back again. That used to be difficulty for your own species(required a psionic AI empire) but might be easier now with crossbreeding. One could test it with kettlings/rackets or spiritualist FE pops as a non-xenophobe. I never tried it myself though it is only hearsay.
In the end getting psionic, erudite and cyborg on your founding species pops and using psionic cyborg xeno leaders might be the most reliable approach though.
Brain slug is a nice trait though but the reduced pop growth speed is not a good thing and slug phopia is -20 stability now.