I actually like the new change, it makes early game interactions with Zagara far less painful since you can “reduce their duration” by simply poking the summons.
As for the list of exceptions, they all make sense.
Nova and Samuro clones’ wouldn’t be good fake outs if they decayed.
Banner, Boombox, and the various Totems are only summons in technicality, they don’t lane or tank hits in lane.
Cannon and Locust are designed to ward/push an area for a set duration.
Wisp, Eye of Kilrog, and Mines have basically no health anyways.
Tychus heroic would suck if you could just poke it twice to eat 80% of its’ duration.