The difference between throwing a pot of Oil on to the ground and lightning it on fire in 5e...
and the current game of BG 3...
Is the sheer *amount* of fire on the ground. Yes, you absolutely can encounter burning ground in 5e. The difference is that it doesn't happen *ever*, *SINGLE* fight. Surfaces don't rule combat in 5e, they absolutely rule combat in BG 3. That and Bonus Action Shove. Literally nothing else is even remotely as powerful. That is the problem.
Surfaces occasionally? That's fine, there are spells that specifically create them and they are a highly unique and costly resource.
Surfaces like they are in BG 3? No, that makes it DoS 3. Stop.