It looks to me simply like the difference between an ‘off the peg’ jacket eg size XL etc. and a ‘bespoke’ jacket. In short an off the peg is never going to be a perfect fit whereas a bespoke jacket made specifically for you taking into account a wide range of your measurements, will be a perfect fit but of course will cost many thousands of dollars/pounds Between off the peg and bespoke lies ‘tailor made’ where a few more measurements than a simple size of chest measurement applies to ensure a better fit. Adding shoulder pads has simply made your jacket a better fit on the shoulders for your build but it’s quite possible it would be a good fit without the pads on another person. Further as others have said, these fit issues are common to any brand and not specific to Aero. If you’re buying off the peg or tailor made the trick is to find a brand or style whose pattern suits your build. For example Lee 101 jeans have always fitted me better than Levi 501’s.
Sometimes an OTR jacket will fit you as well as a perfectly executed bespoke jacket.