That’s not how Upheaval procs devotions (it can proc them even if you have 0% crit chance) - more info here Upheaval devo proccing test results
so in this build Upheaval attempts to proc devo on 52% Savagery attacks
while Storm Spread will have 4 proc attempts on 20% Savagery attacks
so the first one will proc Skellies on 10.4% Savagery attacks
and the 2nd one on 11.8% Savagery attacks according to my math
so Storm Spread turns out to be slightly better in the OP Grim Tools at proccing assuming you hit with with with all Storm Spread projectiles