I 100% agree the Concentration issue is a problem, but how exactly is the damage you describe different from casting Shatter? To me it seems like a semantics argument; as in, if they had thrown the bottle just next to you instead of targeted on you that would have been fine? Or is it the automatic damage from fire? Because that's a feature in PnP...
The automatic damage from fire. What feature in PnP allows a player character to deal guaranteed automatic fire damage to another?
There are a few things in 5e that deal automatic damage with few options for defense. Magic Missile can be stopped by Counterspell or if the target has the Shield spell. Heat Metal is automatic damage (again, stoppable by Counterspell). That's what I've got off the top of my head - I'm probably missing a couple of other automatic damage, but they're few and far between. Most things that would light you on fire (which would then deal some automatic damage if you don't put it out) give you a chance to save against them.
