You ask a few questions which all bowlers who have to watch their spending think of when buying a new ball. I did and decided on what was comfortable for me. Anyone else may have a different opinion because it’s how you value your choice.
As far as lasting longer I guess it’s how much wear you put on the ball (style) number of rev’s, lane conditions, ball maintenance by you, care of the equipment, and coverstock. Some balls may wear out because their softer. There are many factors that can be considered. I had a mid price ball that I had used for 5 season’s before shooting my best scores. Would a high price ball have made me get there sooner, I don’t think so because it took me that long just to get better and more consistent.
If you consider that the high price ball produces the exact same result as the mid price then it’s simple, how do you feel about the ball you purchased? If you feel good about your choice then it does not matter because this will help you to continue to score. If you feel cheated then that in itself may cause a few more bad shots and more bad feelings.
Now consider you shot a 279 or 299 with a 790 series with the mid price ball. One more mark or strike to make the 300 and 800 series. At this point do you think if I had used the high price ball I would have bowled the 300 and 800 series? If you think this way then buy the high priced ball because you could never win with the mid price ball in your own eyes. It does not matter how good you bowl it will never equal what you may have bowled with the other ball.
On the other hand if you know you did your best and there was no room for any luck and as you first stated all is equal the mid price ball was all you needed.
I presently have three balls that I could use for my strike shot. Although the prices were close to the same, one is new and the other two are 4 and 5 years old. Does that mean my newer ball is going to knock down more pins because it’s supposed to be better then the older ones? Almost like high price vs mid price. As I have found out it does not work that way. I have now learned through low scores to use the one that will score better. I may want my new ball to work better but forcing the shot is not as easy as a natural one, and does not score as well for me.
So, I agree with Sceptic it’s both, and also which ball makes you feel better may help you to score better, if all else is equal as you stated.