He allowed an unknown enemy to board the ship, access the ship's computer and then failed to destroy them when attacked.
Next Generation was a very long long way from what I would have regarded as a functional or even plausible chain of command. I think one of the things I liked most about the Original series is that it still had that Naval command officer vibe to it. It felt more like it represented the behavior of an actual warship.
Of course the captain always being on the away team was utter dreck. For that matter any of the bridge officers going ashore seemed pretty unlikely to me.
But still, it had a closer vibe to a real military operation than the Next Generation, or for that matter, anything else ever dreamed up and called "Start Trek."