I think you are answering your own question here. Not to put too fine a point on it, but nobody just jumps into one of those category 3B jobs without, as you sa

I think you are answering your own question here. Not to put too fine a point on it, but nobody just jumps into one of those category 3B jobs without, as you say, substantial hard work and a healthy dose of good luck. You say that to get a job in category 3B you don’t have the experience to confidently pass a job interview. So, keep grinding at your current job until you develop the expertise you need. Or take a job in category 2 that will expose you to the things you need to fill the gaps. Luckily you have the cliff notes to this test - just look at the job description requirements for the 3B jobs you’re really targeting, and seek opportunities that will get that on your resume.