The first Ghisalos are quite flexible. But I love mine. I bought it for absorbing bumps on centuries and it's fast up hills. I bought it because it WAS flexible. They actually made the seat tube larger diameter later on, to add stiffness. I have a tough time imagining a lighter bike being stiffer.
However, the new three piece BB may add stiffness and reduce the weight.
Since it's mainly the shape that adds stiffness just about anything is possible.

Three years ago the medium large was 900 grams. It has been the lightest production frame since then as far as I know. That's what they claim and I can't find a lighter production frame. I don't think they are removing a huge amount of weight from that.

They always had regular headsets.

Edit post: After looking at the tube shapes and reading about it I would believe that the new one is even stiffer. Also my XL size is 990 grams. The New one is 900 grams. Not bad, but not earth shattering, I would guess the front derailleur clamp is probably that much.