some cases 100% is sold and nothing is left in stake.

This is highly unlikely. If it was the case then even with a 50/50 model the price will tank (given your scenario where most people are selling all their token). A 25% increase would only translate to a deeper dip, but the impact of a mass sell action would still be obvious even with the 50/50 ratio

I don't there is no directly correlation between increase in author reward and selling pressure.

It is case between price stability and better distribution.