L2 vs L3/L4 problems prevalence in enterprise networks

Hi there,

I've been working in a NOC for a little over two months and so far the vast majority of problems are related to either routing (L3) or firewalls (L4). L2, on the other hand, seems to just work - I have, for example, not seen a single STP related incident.

I am thus wondering if this is the case for my organisation only or for most setups and what is the relative benefit of further learning about each category of technologies.