I have both primes and zooms, but my core video kit is my:
Sigma 18-50 (now fixed and better than ever)
Canon 70-200 f2.8 nonIS
Constant f2.8, range of 18mm-320mm equivalent.
Zooms are far better for me for run and gun. Less to carry, less frequent changing. F2.8 more forgiving that f1.4 etc.
Just my opinion. The problem is more often keeping things dark when its bright than making things bright when its dark.
Looking for a good nd16.