I'd say that for cantrips at least, you should be able to target a person for direct damage, or target the ground to deal no damage, but create a surface... but you should not be able to damage a target AND create a surface under them with a cantrip with one attack.
Also, if you're going to keep Firebolt as dealing 1d6 damage and setting a target on fire for 1d4, it should tick exactly once and then extinguish - not lingering on for multiple turns. Because it's a cantrip.
I'd have less objection to higher level spells creating surfaces because at least they consume resources.
I agree with all of this. Just wanted to put my voice in the conversation.
