Yes, as pointed out on many debugging stories: problems are easy to find if you look in the right place (hint: knowing where to look is the hard part). Unfortunately for the people living them, there are wireless repeaters and pallets of shampoo that make looking in the right place harder. You might as well have said that Waldo is easy to find if you remove all of the other people on the page.

As for it being "a basic L2 loop that should have taken 10 minutes to track down." If it were a "normal" L2 loop, and he could have taken 10 minutes tracking it down; sure. But when it only happens for ~2 minutes at a time, getting 10 minutes of actual tracking in is hard.

Sure, having managed switches would have made finding it easier. But most debugging stories have something that could have made them easier if done beforehand.