I think if you're evaluating the decision, you have to look at what they might have liked/disliked before going for it. I imagine in the case of Ribeiro GMGM/Oates saw his mind for the game which probably resonated with him. Maybe justified his declining performance with coaching and/or the decline of Morrow. Saw the style of game he played and wanted that type of player to try and pair with Ovi to facilitate the changes there. And I assume saw someone they thought could fit in Oates' PP scheme.
Biggest reason it didn't work (from their perspective)? If I had to guess, again, I'd say it was the lack of fit with Ovi. Ovi transitioned to RW but didn't fit with Ribeiro. Should they have seen that coming? I have no idea. You can't expect them to predict everything, and I imagine chemistry is even harder to predict than average.
Everyone values different things differently, so the warning signs are not universally important. The line between intelligence and arrogance in that respect is quite thin, because both smart GMs and arrogant GMs try to outsmart the market. And both are capable of succeeding (or failing).