wow you sure dream big. i would not know anything about joining a big four tech company. but it seems like you went up from system administration to developer. congrats on that. I think you have worked hard and you are doing very well for yourself. Of course learning to get better at interviews is going to yield results sooner or later. So keep doing that. there will be one day when somebody gives you an offer at a higher salary because of this.

I don't know whether joining the creme de la creme of the industry is possible for somebody who has some trouble with algorithms and the like. it seems a pretty essential differentiator. I'm not very quick when problems get harder as well. But you know whatever. i still eat and i own my home.