Are you doing anything else alongside boxing, or is that your main training focus?
I'd say 2x a week is completely realistic, and honestly, that's what most people do better with long-term than if they start too ambitiously and then quit after two months. Your trainer got it right - consistency beats intensity. If you stick with it, you'll make way more progress over the months than someone who's jumping around between 1x and 4x a week.
The 3-4x a week thing is more for people who can dedicate more time to the sport or where training's just part of their routine. With a job and family on top, that gets exhausting fast, and then both your training and your personal life suffer. Much better to make your 2x a week really reliable, recover properly between sessions, and maybe experiment with some lighter training sessions in between - doesn't always have to be full throttle.