As Droth Malorn says one of the problems with the various versions of the grenades is how they take away from the Medieval / Early Renaissance feeling of the Forgotten Realms.
But the OP is also right and the problem with easily inflicted damage that cannot be defended against will become clear at upper levels when concentration is required for spells. Elemental summoning, for example, requires that the wizard keep concentration or the elemental may attack the party.
Larian just needs to stop making surfaces the center of their thinking -- they managed to do in few instances, the hag fight is perhaps the best example. (also the minotaur fight but I know liking that fight puts me in the minority)
