For a tomelock, would Primal Savagery be as good as Toll the Dead as an alternative to Shillelagh + Booming Blade/Green-flame Blade?
I'd like to have a melee range option to complement Eldritch Blast, but not willing to waste two cantrip slots on it.
Because EB + Agonizing blast does so much damage compared to any other cantrip, it is actually competitive with melee options at low to mid armor classes even with disadvantage.
The break-even point is whatever Armor Class gives a chance to hit equal to the ratio of the melee cantrip damage to EB+AB
So for example at L5 with an 18 CHA and a 3 Proficiency Bonus
Primal Savagery = 2d10 = 11
Staff + Shillelagh + BB = 1d8 + 4 + 1d8 = 13
EB + AB = 2d10 + 2x4 = 19
So the points where EB+AB is roughly equivalent to each melee cantrip option are:
PS = 11/19 = 57% ~16AC
Staff+ Shill+ BB = 13/19 = 68% ~14AC
For Primal Savagery to be better than just blasting with EB+AB you need to be fighting 17AC enemies. Below that, EB+AB is as good or better even with disadvantage. PS honestly does not seem to be worth it unless you are in melee range a lot with high AC enemies.
Shillelagh + BB is more interesting since it kicks in at a lower AC, and the damage rider on BB can boost its effectiveness. The thing to remember is getting Shillelagh off is a bonus action which can compete with Hex (casting or moving). Whether it is worth two cantrip is another question.
If you have repelling blast, EB+AB is potentially even better, since if you hit at least once you effectively get a free disengage, and your GM *may* allow you to make your subsequent EB attacks after the first hit not at disadvantage.