Now.
Cantrips that creates these areas could do so when cast on the ground, therefore foregoing the damage for the effect. I think tjat woulf be a good change. And wouldnt create unexpected situations like burning a web spell.
Adding saving throws to these areas is great as well.
if the surface effects imposed a saving throw to avoid damage, they wouldn't be half as bad. And targetting the ground/an object instead of a PC creating a surface would indeed make sense (and be something I as a GM would allow in PNP too) because it's thinking outside the box and as you say, forgoing the actual damage. But the surfaces should all be imposing saving throws rather than just auto damaging (often for huge amounts)
