I really don't see the problem with the barrels. If somebody has time to collect barrels and win hard encounters with them - let them have their fun.

You don't have to play it that way and as far as I can tell all encounters are beatable without them.

Like, how many encounters actually feature these barrels? From what I can tell its the Goblin Feast section, and two Zhentarim encounters that are full of them.

Compare that to a long list of other encounters that don't have explosive barrels.