We were primarily a possession based offensive team under Keefe. That's different than a rush based team
Majority of scoring chance from keefe system was coming off the rush and was agressive on transition, resulting in a lot of turnover against ( where let's the leafs beat themself) After blaming like marner, nylander, matthews for those missed on transition but it was the system who was like that.
When leafs having the puck in offensive end and attack of the rush didn't work, yes they became possession team with cycling unstead space open up somewhere. With D doing minimal of thing in the offensive end ( except when trailing). Trying for the perfect play over and over again and basically never taking shot with D. So team just let leafs skating in the outside and protecting the middle and it was over .leafs D was basically never involve come playoff time offensively so its like leafs playing at 3v5 on a possession game
For me they are 2 way to see possession style.
1- Try to keep the puck as much you can when you got him( pretty close of what leafs did under keefe). You get the puck a lot when you got it but leafs was playing much more when they was without the puck before trheybwas struggling to get the puck back
2- Try to get back the puck as much you can by winning puck battle ( closest of Berube system). When you've got the puck you playing less with but at the same time playing less without by winning more battle.
So sorry, im not really sure if keefe system wqs really better for possession especially against good team, where leafs was losing most of the time possession battle.