You can argue with its execution and how they handled it, because they really should have executed it better IMO and put more time into it and built it up more. But in the comics, Slade's motivation is also a dead loved one. The reason Slade went after the Teen Titans is because of the death of his son Grant, which he blamed on the Titans. In a similar manner to the comics, the death of his loved one was also someone else's fault, but he put most of the blame on one party. In the comics, H.I.V.E were also responsible for Grant's death, because they gave him a formula that enhanced his abilities, but in the end it caused him to burn out and die, but he still put most of the blame on the Teen Titans. In Arrow, Ivo was responsible for Shado's death, but he put most of the blame on Oliver, who he considered to be more at fault.
He was also hurt because he considered Oliver's "treachery" to be quite hurtful as he viewed them both as brothers, and he spoke before about how much loyalty means to him after Billy Wintergreen betrayed him, another person that was very close to him and who he made the godfather to his son (in the comics Slade and Wintergreen were very close too, as they both saved each others lives at different points and Billy stood by Slade, even after he did horrible things that resulted in him getting divorced).