I don’t think having one Palpatine line makes it obvious that Palpatine is the one talking to him. I mean, we would hear Palpatine, Vader and Snoke, so arguably Vader (or the dark side) is just showing him a vision of different voices and events. It could arguably be just frame it as a memory of Vader’s, when Palpatine said that to him in ROTS. I also think Palpatine’s line is sort of important to contextualize Kylo’s belief of the Jedi philosophy being destructive to stability and order.

But, alternatively, you could potentially use these Vader’s lines instead:

(Construct this line) Vader: Destroy the Jedi.

Vader: End this constructive conflict and bring order to the galaxy. It is your destiny…