Yesterday wasn't about the rules. And what I said makes perfect sense .... Walker shouldn't have been concentrating on playing a single player offside then there are 9 others he should also be concerned with. So what if that player was offside ? Common sense says that unless you know 100% for sure he is the furthest most forward player (which defenders facing up the pitch, and not looking into the stands, would know) then you can't assume he is the only player you need to play offside.
But to come back to your point - which I think I just covered above. Other than that the old offside rule was a horrible rule that used to spoil many games - players that would have not influenced play in the slightest were given offside destroying many otherwise bona fide attacks. This rule may not be perfect but it's light years ahead of what came before.
I get Ibro's point which I think is that Grigg is influencing play because Walker knows he can't leave it even if the player is lingering off side. Walker couldn't not be concentrating on a player who was offside because he can become onside very quickly such are the new fucking weird rules. I agree that it is better than flagging for any player not influencing - but there is no common sense applied to a lot of the decisions under the current system.