Yeah, the two are completely different mechanics. About the only thing they have in common is that everything that used 3e concentration also uses 5e concentration... but then, almost everything with a duration in 5e uses concentration. It probably is a good way to rein in caster power, but it'd be very difficult to backport, since it'd have to be done for every spell individually (the fact that it applies to almost all spells with durations would make the decisions easy, but there are still exceptions, so you'd still need to make thousands of decisions).