I believe 1 to 2 was just a name change, so I doubt there was much difference there. 3 introduced a new game engine so there are code differences, but I find it hard to believe HTC would've let that change mechanics or physics.
All changes, major or minor were documented in patch notes. There would be no reason for HTC to make game altering changes and not document it. In recent years, some changes have been made to the MA but they are strictly arena setting changes that can be viewed by anyone (hardness settings, for example).
Bomber gunning has not changed. There was not and is not a reason to change it. I believe something happened that you didn't like, so now you carry the narrative that the game changed because you aren't as good as you thought you were. You have no facts or proof, just the subjective opinion that it changed or was nerfed.