Virtually no one claims that ground effects have "no business in D&D", most of us are quite aware that D&D has a lot of ground based spells like Spike Growth, Grease, Web, etc. as well as items such as Alchemist's Fire or oil/acid flasks. What D&D DOESN'T have are cantrips that deal damage AND create a surface effect in addition or even on a miss. Of course throwing an oil flask with your rogue and having your mage set it ablaze with Burning Hands or even a Firebolt should remain, no one is arguing that. But a Firebolt that creates a fire ground effect by itself is a bit much, not to mention the general overuse of such effects.
Exactly... using thrown items or spell effect combinations are very valid low level tactics, but they are usually just that. A low level party shouldn't be able to turn a whole courtyard or goblin camp into a hellish inferno, using a cantrip and a few jugs of oil, though, that's what high level spells are for. Why even have character progression otherwise?