Hola @SilvyC
Yes, Radicchio is originally bitter, that’s why we have a so long process with resurgive water to transform the plant in something delicious.
The same, or equivalent process, is used all over the world also for other vegetables. Have you ever tried to eat a raw olive? If not, don’t try … I am sure @KarenVChin will be happy to share her experience with you about that.
I was trying to see if Piola (Libertad 1078) have radicchio in the menu, but looks like they haven’t too. I was used to go in the original pizzeria Piola in Treviso, and of course they have Radicchio Pizza (They call it pizza Treviso, of course