Obligatory just got fired post.
A three month ramp-up period in an infrastructure job? Even in fairly simple environments most people would need six months to be competent. Sounds like they just didn’t like the person for other reasons or wanted the proverbial purple squirrel and didn’t get that.
Because I was born lucky (big brain) and have a lot of experience of my company purchasing and then me and my team integrating other company’s infrastructures, I’m exceptionally good at learning other environments quickly. I can generally learn a new-to-me environment in 2-3 months. But of the IT people I’ve met, for most it takes 6 months to a year. In that area I’m one out of a thousand. If that sounds arrogant, well, good for you but it is the truth*.
Three months is just not long enough for most people and I would not expect it of anyone.
*I worked at a hosting company with a very complicated environment. I learned it in three months to where I was doing large projects completely on my own. Most people there were only assigned any sort of project after six months and large ones only after a year. My manager said he’d never seen anyone ramp up that quickly.