They should just get rid of the barrels, there are pre-existing items in 5e that does the job - i.e. Flasks of Oil, Vial of Acid etc.
Smokepowder, Firewine and Oil Barrels are essentially transforming everyone to a 5th level Wizard with Fireball. It's too strong. For instance, the amount of Nautiloid Tanks you can grab in the intro allows you to one-shot the 2 Cambions and the Commander if you drop them before activating the 2nd wave of Imps, then proceed up the stairs on either side and hide once you've killed off the imps. The 3 devils will stack around the Mind Flayer and you can then proceed to use a candle, a scroll of firebolt or goat the Commander into hitting the tanks himself using a familiar. An extra 100 xp and 3 greatswords is what you get from your troubles, meaning once the next cutscene is over, you hit level 2 with xp to spare.
