Obviously if the op was gaining weight at 2000 calories it was a bad estimate for him (or he was eating more than he thought, which is often the case), but it isn't a crazy estimate or anything.
The problem is not the estimate per se, it is that people don't understand what terms like sedentary and active implies, and tend to overestimate how active they are.
E.g. the vast majority of people who work office jobs are sedentary, whether or not they think that their out-of-office activities makes them "active". An hour of activity here and there in the evening does not get anywhere near compensating for 8 hours in a chair.
This, to me, is another reason why employing a feedback cycle and only relying on those estimates as a first approximation makes most sense.
The estimates won't take into account how dilligent you are: do you estimate how many meatballs there is per 100 calories, or do you guesstimate based on measuring once? do you count the calories in your sugar free chewing gum (it's certainly not calorie free)? do you measure out the amount of ketchup you put on your food and count the calories? And so on.
With a feedback cycle hopefully you're roughly consistent, and if you adjust on a weekly basis based on how you're doing you'll hopefully also counter-act your own self-sabotage (e.g. it's oh-so-easy to subconsciously take more of anything you've decided doesn't need measuring, like the above mentioned ketchup, or find yourself suddenly chewing 10x as much chewing gum...)
(at the same time, one of the benefits of these shakes certainly is that if you adhere strictly at least for periods, you take dilligence out of the picture; though you still need a feedback cycle, as e.g. differences in how much energy you have can easily affect your activity levels and so change your rate)
What matters is not what the average burn rate for your build is, but what you burn. And you yourself is the source for that calorie intake being too high for you.
The averages matters for generc advice and as a starting point, but they can never be as good as measuring and adjusting.
And I think that is part of the problem with this advice. Too many people seem to influence their intake by it but then get surprised and dejected when they don't get the result they expect, instead of using their result to tweak their intake accordingly.
Overall I think the typical old advice of 2500kcal for men and 2000 for women are dangerously out of tune with modern lifestyles.
As your own results demonstrated, that's often way too high. Measure, weigh, adjust - ultimately the only thing that will tell you what the right amount of calories is for you is to actually adjust your intake and check what happens.