For me, three is plenty. Given the cynical way subs are often used i'd be struggling to see the overall benefit. An extra few minutes more lost to each game where the ball is only in play for not very long as it is. If you're going to have five then you either need to make games longer or ban the use of subs in the last ten minutes or something because far far too often they are used as nothing more than a time wasting tactic..
I see your point and i hate the last minute subs...
The five subs rule means that you cant have five individual subs. I think three need to be at once, and the other two can be done individually. So essentially it is the same as having three subs now in terms of time. But I take your point that generally it is a time wasting tactic - the referees need to make sure they add the half a minute. Dont trust em though to be honest