Having cantrips only create surfaces if targeted at the ground seems like a fair middle ground. Firebolting an enemy is a normal 1d10. Firebolting the ground leaves a little flame patch. I'd also be fine with full 5e, no surfaces from cantrips at all, but different behavior for targeting ground vs enemies seems like a compromise.
I love this compromise, and this idea reminded me of a certain druid cantrip. "Produce Flame" would be a perfect cantrip that allows you to make a fire surface, in PnP it kinda sucks. You take an action to make fire, and then you have to spend another action to hurl it, which is really firebolt that costs two actions to use. Now creating fire surface would be interesting.
