Surface effects could be easily balanced by just having any fire surface have 1 turn duration and do less dmg. *snip*
Disagree, that isn't an easy balance. Even doing just 1 point of unavoidable damage is too much because of Concentration, which is a *huge*, absolutely *MASSIVE* limitation to control spellcasters from getting out of control (like in prior D&D editions). Even just 1 point of unavoidable damage = Concentration Save (it's a save not a check damn it). That is part of why unavoidable damage in 5e is so rare and usually has a large costs associated with it (primarily from spell slots or other limited class resources). Unavoidable damage makes Concentration spells significantly less useful, which throws a ton of other things out of balance.
