The whole "bullets travel in an arc" seemed like BS until I actually tested the point of aim / impact with different weight bullets.

POA and POI are definitely affected by distance, charge and bullet weight !

This is why I can not agree with those that would rather use a tight rear notch/front post as opposed to the ability to adjust the sight picture for compensations ...

I am talking target shooting here, not defense shooting, I would rather have the tight looking sight picture no matter what the distance when fighting for my life !

To add to my earlier comment please remember one extremely important point. The EXACT same round will "feel" different to different people and will act differently with each. Not to start some huge discussion here BUT, none of us grips exactly alike, pulls (squeezes) the trigger alike, nor any of the other variables that are out there. I suggest starting places to my students based upon what they tell me they are after in the performance of a round. Lastly even Glock will say that no two of their firearms shoot EXACTLY alike; the differences may need to be measured by machine and not man but that is the simple truth about machines. This is also the reason that all the stats that are printed out by bullet manufactures are based on being fired from a "TEST BARREL" so they can eliminate as many variables as possible. Bottom line, shoot what feels good to you and gives you the results you are looking for or as my wife once reminded me "you have to kiss a lot of frogs before you find the Prince".

You are correct about them being "machines". A well built and well maintained machine will give years or acceptable service.

+ 1 Glock !