The difference is that the caddy is an integral part of the game since its earliest beginnings. There is miles of diffference between a caddy and an artificial device. The spirit of the game is that is always been the golfer, with stick and ball.
The rules have always prohibited artificial devices, and there was no blurry lines. The introduction of the DMD has blurred that a bit, but the principal remains.
And for the suggestion that caddies shouldn't give advice is never going to happen, as that would be ridiculously hard to police at all levels of golf.
You raise some interesting points.
My research suggests that caddies started initially as forecaddies to find the ball for a golfer, which in the beginning were prohibitively expensive ( a weeks wages) Had these players had technology to find the ball you can be assured that they would have.
This had nothing to so with the spirit of the game but pure economic sense. Cheaper to hire a caddie then lose a ball. Nowadays it is cheaper to run an app then it is to hire a caddie ( that basically don't exist in many places anyway. )
And are their really that many differences between the two?
Both give yardages - the caddie remember used a gps before the day to record a multitude of distances.
They both can recommend the club to hit.
They both can advise the the golfer of the wind direction.
They both can tell you whether the pin is above or below your ball.
They both help you count your score.
One carries your bag the other you carry in your bag.
But only one can read your putting line, line up your ball on the putting green, talk to you about your swing, remind you to have a drink and then gets it for you etc.
Really, if you had the option you would have a caddy, if it was only someone to talk through and seek a second opinion on your thought process etc but for all but the elite and the very rich it is no longer an option. (It wasn't always like that btw, my part time job as a teenager in the 70's was caddying at a country golf club, $ 5 to $6 and a drink for the round. There were ten of us and always a morning and afternoon booking.)
I agree, you can't police caddies talk, so we allow it. The DMD box is already open so let it happen. Providing it doesn't slow play, give the golfer as much info as they want from the App Caddie. Ban them from professional golf or club championships if you wish but for the run of the mill event who cares. That would be in the spirit of the game.