It really depends on your use case.
NOTHING plasma based hits as hard as plasma seekers at rapid fire in a single turn of firing. So in a legion that can deploy them as such, they can be very good. This usually means in a pod, or infiltrating/outflanking in a rhino.
Naked seekers are very efficient as a AP2 anti infantry platform.
Plasma tacs are great for sustained plasma use over the entire game.
Plasma vets open up some opportunities for certain legions with outflank and they can often fill a compulsory troop slot.
So in short, yes they still have a great place in the game. In my Raven Guard force, I use them all the time for turn 1 alpha strike, and they are the best plasma unit for this.
With other Legions, your use might vary, but the scorpius bolt totally did not replace the single turn damage output and range of units that a combi plas seeker unit can absolutely demolish.