I was reading the amp cantrips and the terminology confused me a little, basically I assumed before reading the amp description that the effects of the amped cantrip replaced the original. So an amped telekinetic projectile would do 1d8 per level damage instead of d6.
But the wording of amp could be interpreted as getting both effects (the 1d6 per level and the 1d8). Obviously thats too good to be true so it might be worth doing something with the language to show one effect replaces rhe other.
I think it's pretty clear that you add the effects of the amp to the cantrip.
When you cast a psi cantrip, you can amp it by spending 1 Focus Point to add the effect described in the spell’s Amp heading.
In the case of TK projectile, it makes it clear in the wording of the amp itself that it replaces 1d6 with 1d8
The damage changes to 1d8 damage
at most, they could maybe say "add the effect and replace effects where specified" but that seems unnecessary to me.
looking back over it, there may be a few instances where it is less clear (though so far I've found 1). The amp heightening of shatter mind makes it unclear if the rend heightened replaces the regular cantrip heighten. Considering no wording here says the heightening of the amp replaces the heightening of the cantrip, I read it as they stack.