I know what you mean, but its still kinda funny.
I knew when I was writing that, that it read weird :P
You always come back to "you can beat it by just following these steps". But it still isnt the point that you can beat it. The point is, that is not balanced in a way that makes all play styles equally viable. This is something that 5e is good at. Not perfect, but really good. There are ups and downs, and the later levels get a little whacky, but the balance between levels 5 to ~12-15 is good. And that class balance is held alive by things like bounded accuracy, saves, AC and concentration.
Here is the fundamental difference between you and me I think. I do not believe that all styles of gameplay should be equally viable. In a tabletop game, if a group of level 1 adventurers attacked a dragon head on, would the GM have them win the fight? More likely the GM would have them all die a horrible death. Imo, some approaches to combat should be doomed to fail horribly. The thrill of overcoming all the failed attempts where tactics were insufficient for the fight is part of what makes challenging battles enjoyable to me.
And those things get positively broken by unavoidable damage through surfaces. Look at the mighty firaball. 20 foot radius of pure fire carnage. Even here you get a save to avoid at least the full force of it, while some classes even can avoid it completely. Not even the mighty magic missile spell, a spell that is by design always hitting is unavoidable (hello shield spell).
Then adjust them, allow saves against the damage, limit them to certain items or even as you pointed out below, the "create bonfire" spell. Nobody here is saying surfaces have to remain exactly as they are, I am just saying I don't want them gone.
Why would anyone learn the Create Bonfire spell? It is just a strictly worse option, when I just can buy some firebombs, that cant be avoided and dont require my concentration (not that concentration would be up for longer than 1 round anyway). These things actively invalidate spells and effects that 5e already brings zu the table. But 5e does it better.
Homogeneous balance is balance of the worst kind. It removes all of the flavor from a setting.
