This stuff may happen, I can't say it is untrue, but I've never seen a manager terminate a decent to good programmer because they didn't understand their workload.

The companies I've worked for spend a lot of time recruiting talent. If a manager wanted to can someone because they didn't know that fixing bugs takes time, it would be the manager in front of a more senior manager demanding they explain their logic. Also, if you've managed programmers or SW projects for any amount of time, you'd understand why things take time.

Most folks I've seen get terminated is because the company is shrinking, or they are not performing or they are a jerk and/or violating company policies.

My thoughts are do the best work you can, be nice to others and you'll be fine as long as the company is making money. Don't worry about 'metrics', people generally know who's worth keeping based on more than that alone.