There can be various ways to decide the match winner in a tie game, especially in the final match. The result of a cricket match should be about the runs made and wickets taken and not about the way runs were made or wickets were fallen.
As all of you know, NZ scored 241 with their 8 wickets fallen and ENG were all out for 241 and the super over was also tied, that means neither one of the team won nor lost and both the teams were equal. And world cup should have been simply shared between both the teams. But in the end, it was decided on the basis of boundary count and as a result ENG emerged as new world champion.
I don't know how one team would know that how much boundaries they need to hit before the start of the match because not in all the cases, but in most of the matches where the chasing teams wins or where the scores are level at international level, then generally, the boundary count of the chasing team is higher than the batting team who batted first.
But if it is necessary to decide a match winner(if super over is tied), then some options are available like:
1) Continue the super over until one team wins it.
2) The league stage performance(like most points, good run rate,etc.) should be consider,etc.
And in the game like this, third umpire must tell the on-field umpires on the spot if any wrong decision is taken by them like rewarding six runs instead of five runs.
NZ really played brilliantly and captaincy of Kane Williamson was praiseworthy, but the rules made them and their supporters disappointed.
All the best NZ for their future.