IMO, there is a world of difference between backstopping and the question of advice.
I believe the rule requires a player to mark his ball on the green IF doing so can be accomplished without undue delay. (If my wording is incorrect, I think that gets the gist right?). That creates a ton of judgement calls already; even if I’m close to the green, should I sprint to mark my ball if another player is already preparing to play his shot? If I’m not mistaken, the current rule is a one-way rule, isn’t it? It requires me to mark if I can do so without undue delay, but it doesn’t require another player to wait while I go and mark my ball.
Any attempt to add to that rule brings even more judgement into the equation. How close to the hole? How close am I to the green? How close to the line of play? And so on…
I will cop to going ahead and playing my shot before a fellow competitor has time to walk up and mark his ball, but only when I was already closer to the green to begin with. I don’t hurry to play the shot; that would be counterproductive vs the remote possibility that my ball MIGHT hit the other ball and be helped by that more than if I just played a good shot to begin with. I realize the pros are far more precise than I, and it bugs the heck out of me that this practice goes on, but I don’t know how you legislate it away without creating even more issues and slowing up play.
The club selection thing, by contrast, is relatively cut and dried. Either advice was asked for/given, or it wasn’t. Looking away with a wink and a nod, or saying, “Well, everybody does it…” doesn’t change that.
I’ll say it again; I struggle with the concept of these guys in ANY way assisting a guy they are trying to beat. I just do NOT get that, and I’ve been in competitive sports for 60+ years now. It is beyond my comprehension.