The genesis of today's game did not start with Cody's Kilkenny, to see why we are where we are today you need to go back a couple of years.
Up to 2003 hurling had been played pretty much 15 on 15, players playing to their positions (win your own position and that is your job done). Donal O' Grady revolutionised everything by introducing the running short passing possession game, and this was a winning game plan, To counteract that Cody introduced the massed/packed defence and it worked but more so it worked even better against teams that still played the traditional orthodox way. Blaming Cody is a bit myopic as KK would never have played that way (remember they had won 3 out of the previous 4 AI's) if O'Grady hadn't changed things up to begin with.
Limerick under Kiely (but more so down to Kinnerk I would think) have adapted the Cody KK approach of funnelling players back when they don't have the ball and the O'Grady Cork approach of playing the short passing possession game when they do have the ball. So basically their game plan is an amalgam of the tactics used by both Cork and KK in the early noughties.
Just to clarify I'm not blaming O'Grady just pointing out he was the first to revolutionise the game and that has ultimately led to where we are today, however a coaches job is to win and he did that, all games evolve and if he wasn't the first to tear up the previous script someone else would have, especially since the trend in recent years of coaches from different codes sharing ideas, attending courses etc.
If you look across all team sports the tactics are all becoming very similar, close down space, keep possession, work hard etc it's not unique to hurling or Gaelic football, soccer, rugby have gone down the same route, its just the group think that has perpetuated all sports most likely from coaches being more open to taking ideas from other codes and the fact they are now attending all these coaching events and mixing and sharing ideas with other codes.
If I had to name one sport which I think all others have borrowed from, it is basketball. Defend in mass by pressing hard, and then, if you turn it over attack in mass at pace.