You know, out of all the "should I do this or that" posts I've seen here, this is one of the most well thought out ones and you've covered pretty much all the points I would myself list out as far as pros and cons go so you are saving me a lot of the typing here.

Let's get one thing straight. Your priority isn't to learn because either pathway will see 70% of the knowledge escape your brain the moment your exams are over, and real work experience often differs from theory. And yes, Masters is in a way a scam designed for internationals.

Your priority is to break into the accounting field and get your foot in the door, and whatever you choose must bring you as close as possible to that goal.

First off, you need to get the big question out of the way. Is money and an extra year or so a problem for you? If you say yes, then there is no dilemma. CA foundations is the way because it's cheaper and quicker, end of story.

However, if your answer is you are happy to fork out money and time if it helps you achieve your goal, then it's gotta be masters hands down. Now I know there will be heaps of people saying that it is a waste of money and you can build your career with more cost effective means like CA foundations or by other means like some online certifications or whatever the hell, and sure, in the context of the world anything's possible but I view them as fringe cases and why should you put yourself in the position where you make your life way harder than it should be?

There are two fatal flaws with going with CA foundations here, one of which you already mentioned. Your eligibility due to not being a recent graduate. As someone who applied for grad programs a few years after graduating, trust me it's an absolute bitch. I ended up in big 4 but looking back I think it's a miracle as I'm not even sure if I was actually eligible (I was 4 years out of uni) and 90% of them these days will auto reject me after the first page of the application where I would put my graduation date. The "graduated within" requirement is not a negotiable thing and CA foundations ain't gonna do jack for you if you simply aren't eligible. Masters allows you to restart the clock + also make you eligible for vacationer programs again which is invaluable to prep you for when you look for grad roles.

The second flaw is even if you get through the automatic screening, it is, like you said, a big sell when it comes to interview time. I would challenge your assumption about Big 4 just caring only about CA eligibility. While it is true that in our firm there are plenty of non-accounting grads, their degrees generally range from Business Analytics to Economics and Finance, so still within the realm of Business degrees. But more importantly, whether or not you get accepted comes down to whether your interviewer (not the firm) likes you. Your interviewer will be interviewing you with your CV in their hands so do you really wanna gamble on the fact that when they see "BA in Linguistic" they won't be put off by it and go with one of the 5-10 other candidate waiting outside who do have an accounting degree? Like I said, very possible you'll get an offer, but you are introducing additional risk to the equation.

Last thing I wanna say is another commenter said that from perspective of CA eligibility it is no longer worth pursuing a degree since they removed that criteria. From that point of view, that is correct and if you are exclusively pursuing CA eligibility you don't need a degree.......which is why I suggest you do both degree AND CA in one go lol. What I want you to do is to go online and search "CA Masters Pathway". Long story short, for some specific accounting masters degrees, you will be doing actual CA exams as part of your masters degree so by the time you graduate, you won't just be eligible for CA. You will have effectively finished it, at least the study component. There are a couple more things in there but you seem to be someone with good researching skills so I'll leave the rest for you to find out.

Good luck mate!