it just works so well that kylo confronts his pull to the light in TFA and then kills his dad. embraces the dark side of the force. helps kill billions. and then his actions in TLJ are just him manipulating the situation to get what he wants as he's able. he wants to kill snoke. he wants to kill rey. he still wants power. and it's all going exactly to plan until a conflicted rey has her light/dark confrontation and rejects kylo. then we see the person kylo's been hiding from rey in all his fury.I think the issue is they had a light/dark conflict with Ben and did absolutely nothing with it. He turns out out to be a stupidly written character as a result.
and yeah, all of that completely gone and wasted in ROTS.