Another solution to the problem of not being able to turn off the visual effect if all 3 PVE legendary trinkets are equiipped.. is to change the visual itself.. (which with 3 of them some find ugly.. but more importantly a visual clutter).. change the visual to --
1 PVE legendary trinket = 1 glowy ball (same color as single trinket like vision instead of 4)
2 PVE Legendary Trinkets= 1 (or 2) glowy balls with significant color change.
3 PVE Legendary Trinkets = 1 bigger ball with color change
less visual clutter/noise .. rectifies the ugliness of the 3 trinket effect (subjective to some). this maybe an easier fix than tweaking all that "buff" aspects and behind-the-code aspects of the PVE trinket set visuals.