I don't rely much on stealth, I rely much more on [...] line of sight.
I know what you mean, but its still kinda funny.
Melee enemies can't catch you when you are using expeditious retreat and ranged enemies suffer against line of sight. Choke points are the tool for dealing with crowds, narrow corridors and doorways are all over the place in the arenas provided to us. The question really is, what constitutes "normal" play. Obviously, you do not balance the game around optimal gameplay or mechanics abuse in the case of reload cheese, but you should not balance the game around someone who is hitting the end turn button without doing anything every single turn either.
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.
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).
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.
