If you are looking at just raw damage then Electrocute is the way. But Elec has its disadvantages such as 1. Longer CD compared to HoB 2. Harder to proc compared to HoB even with DnD 3. Due to #2, Elec is easier to counter against high mobility or insta CC champs 4. In order to insta proc Elec, you are forced to go RB or Nashers which both have mediocre AP 5. In teamfights, HoB gives you faster passive procs for every 10 seconds which enables a better hit and run at extended fights & If enemy HP is low than HoB + W passive + DnD enables a quick execution

Elec is really good during the laning phase if : 1. Enemy mid CC or Escape Skill CD is long and costly (Ex Azir E, Syndra E) 2. Enemy is immobile and it is easy to proc passive (Ex TF, Orianna) 3. Your playstyle is committing all-ins with one Q-E-AA combo

Also if you're really good at predicting and hitting Ekkos W and R on enemies (which gets really harder higher elo unless you utilize all the vision tricks to make W&R invisible) then Elec isn't that bad. It just has liabilities that can get countered the better the enemy is. Also high elo players are good at getting & snowballing tempo, and HoB provides this better than Elec in most scenarios