Jaques
I have been having a look at your pictures of the hub.
What type of bearings do you have for the blades to twist on? You have a lot of backward thrust and a lot of radial force so the bearings need to be free with these forces present. I couldn't tell whether you have any form of thrust bearing to keep it free with radial load.
Your weights are a fair size but not at a particularly large radius so you may not have enough force to overcome friction.
I suspect that if you spin the hub alone it will work fine.
I also agree about the slide needing improvement. To keep the blades tracking properly that slide needs to be a reasonably long sleeve on a smooth shaft. Also at the point shown in one of the pictures the linkages are only at a small angle to the allthread and the blades could twist independently quite a bit.
With your blades mounted well up to the leading edge I don't think you can do much more about blade pressure, I think its more force or less friction.
I am sure you are not far from success
Flux