Hold for Reinforcement has added several options to try and manage Coyle. I find that letting him chase something off to a corner, then knocking him out and turning him invisible works reasonably well. But even then, he can still be one shot by random agro. Your actions can reduce the chances of bad luck causing failure, but that unlucky one-shot-kill can still happen.
The Ogres, on the other hand, do target the named one. If you are failing the quest without killing the spider minions then you probably left some ogres alive in that shrine room, possibly on the hard to reach ledge. I suppose that with a little stretch of the imagination one could suppose that they might finish the named spider off while you are fighting the end bosses, giving the impression that something else actually happened there.