I gave splash a try with Heavy Strike and was pretty underwhelmed.
With a 5 link which has **faster attacks -added fire damage-melee phys-weapon elemental damage-heavy strike** I get 7857 tooltip. Take weapon ele damage off and it drops to 6694. Replace that with splash and it goes to 5354. Pretty rough. Granted, this is without splash leveled up. I just added weapon ele damage in and that isn't leveled either.
Reduce that 5354 by 50% and it's a 2.5k AoE which isn't horrible. Compared to my sweep which is in a 5 link and does 1.4k and it's looking pretty good. But the thing is, I also have culling strike and IIR/IIQ gems on sweep.
I can almost see a situation where I could be switching to sweep when mobs are almost dead, but that would need enemy health bars on screep to really be effective, but sweep has such a nice AoE radius and is almost 360 degrees. I'm thinking multistrike might actually be good for my build, but I'm not expecting to find one of those any time soon.
Edit: It looks like melee splash gets +3% melee physical damage and -1% less damage to other targets per level. So at level 20 it would be +60% physical damage, -20% to main target, -30% to other targets. That might actually be pretty good. For now I'll just keep leveling it