I do not know whether or not have a practising certificate opens particular doors or not, but I would be surprised if it did outside of the legal profession. The reason for that is that it is literally of no practical use unless you are actually practising as a barrister. The world of being a barrister is quite insular to a degree, and it's hard to even have a conversation about it with a lay person without stopping every few minutes to explain what a particular term means. The average person wouldn't have a clue what is meant by the BPTC, chambers, pupillage, tenancy, a practising certificate, or any number of other terms. It reminds me of an episode of the apprentice where Alan Sugar asked one of the candidates why he shouldn't fire him, and he replied "I got an Outstanding on the Bar Course". Alan Sugar just looked at him and said "I have no idea what that means", and went on to fire him. Which illustrates why unless you're planning on staying within the law and practising as a barrister, perhaps in an in house role, I genuinely do not see how having a practising certificate would open doors for you.
It's clear that you're struggling here, but the issue of whether things can be made for bearable for you is a different one to whether or not you should continue with the pupillage. Something is clearly fundamentally wrong if you're two weeks in to first six and you are hating every minute, especially when you speak so well of your set and pupil master. It may be as you say that and this profession really isn't a fit for you, but no one else can ultimately answer that except you. I don't remember whether I was one of the people that advised mirispoonie to continue with her pupillage (I'd like to think my advice was more nuanced than that, but it may not have been), but it is pertinent to note that whilst issues were identified and improvements were made to her situation within Chambers (some of which we identified in our conversation), those improvements didn't suddenly mean that she became suited to a profession that she ultimately didn't want to continue in. Making changes to your situation within Chambers can only ever put you in a position where you can better inform yourself as to whether or not this is the right path for you. It cannot make it be the right path if it isn't.
So ultimately you need to make the decision that is right for you here, but it is right that you are looking to gather views and inform yourself before making that decision. To that end I am more than happy to talk with you if you want, as I did with mirispoonie and have done with several others in similar positions over the years. I cannot offer solutions, but I can listen and I can give you a sense of perspective as to how normal or not your experience is. I can also potentially answer difficult or sensitive questions that you might not want to ask people that you actually know. No pressure of course, but the offer is there, and if you do want to chat just PM me.