"If we turned the top 20 consensus witnesses into the top 100 consensus witnesses, we gain decentralization, but perhaps we lose security because the top 100 are not as trustworthy."
"For the most part, decentralization and security are linked at the hip."
It seems to me that the above two statements are contradictory. If the odds of any one witness being untrustworthy is X in 100, the odds against a majority of witnesses being untrustworthy are far higher in a pool of 100 witnesses than a pool of 20. While an individual witness may be untrustworthy, the impact of one or more untrustworthy witness(es) is much reduced in a larger group, which supports your latter statement that decentralization increases security.
Perhaps looking at the inverse, the odds of a witness being trustworthy are X in 100, changes this calculus? But then decentralization decreases security as the following statement indicates.
"...centralized leadership during a crisis can sometimes be the difference between life and death."
So much of human society cannot be reduced to such simplicity as the above equations attempt. Quantity and quality aren't comparable. From observation I note that centralization always proceeds from decentralization, and eventually produces inequities that cause destruction. Fortunately I believe my anecdotal experience is inadequate to assert confidence, and my observations are wrong.
"One could hope."
I have faith.
Thanks!