When 5E was designed there was a central philosophy called "bounded accuracy". To summarize: the game design is
extremely strict about things which can actually damage HP.
- Attack Roll - Most damage requires an attack roll. The accuracy of this roll is bounded by a fairly strict level = value. Even many spells were switched to attacks in this system. To compensate spell casters get proficiency on magic attack rolls and include their stat in those rolls.
- Saving Throws - If a spell doesn't have an attack roll then it will almost always have a saving throw. Usually for half damage and sometimes for null damage. The rolls required for these saves are bounded and strict just like attack rolls.
- Direct Damage - This is stuff like magic missile. It always hits and always does full damage. These sources of damage are very unique and almost all of them come from "limited" resources like spells. These sources on a per level basis do less damage as well.
Everything in the game is balanced around this. The amount of healing you get, the defense against damage, the amount of resources you have between long rests. All of it is balanced around this core concept. So when you throw fire on the ground everywhere and it does large damage per turn without a saving throw or an attack roll this balance is flushed down a toilet.
1. Cantrips are meant to be weak spammable spells. In no way should they create dots or surfaces. They are supposed to be weak(with the exception of Eldritch Blast). By adding a surface to these spells you are causing them to be the equivalent of level 2 spells.
2. The sheer amount of "surfaces" are out of control. They cause a loss of resources and HP that 5E wasn't built to support.
3. The surfaces need to allow defense via the above rules. Saving throws with low DC for null damage should be the norm for something so common. Powerful things like restriction should be rare. Etc.
TLDR: 5E isn't supposed to have this much crap on the ground. Reduce it. Add saving throws. Stop breaking the balance.
