EzekielRaiden
Follower of the Way
It doesn't need to be perfect, but it can be much, much better. Not being able to reach perfection is not an excuse for not trying harder.1. The "system" for determining difficulty of a challenge is close enough in my view for the average party with average players. It's not perfect, sure, but nothing will be because
You don't need to account for all of them. Just enough of them. Throwing up your hands and saying "well, we can't do infinite things, so there's no point in even trying to do any things" is clearly not the right answer.2. The level of difficulty of an encounter can change the moment the players start making decisions that impact it, and no system can account for all of those variables. So
Or, as an alternative: have those things and a reasonably-comprehensive (but self-aware of its limits) system.3. Have a plan for what to do if PCs die (e.g. backup characters) and a system in place for resolving the PCs' retreat (e.g. chase rules from the DMG).
Understand and do these things and play on.
The fact that you might wander off the map is not a good reason to abandon cartography.