No, Theo is not perfect. He has made his share of mistakes, and paying big prices for relievers is one of them. The ironic thing is that after Foulke, I'm pretty sure he commented about the mistake of signing relievers to big deals. That said, he is still the GOAT.
FTR, when Theo signed Kimbrel, I posted in that thread something along the lines of "Theo has lost his mind."
These GMs should listen to me more often.