Well, just as a point, very, very few enemies are intent on pursuing the party until they are all dead. Most opponents would be perfectly satisfied with chasing off the party. Claims of realism are a tricky thing at best.
Then again, baddies that always fight to the death and never surrender is one of my personal bugaboos. I do wish 5e had morale rules.
No Kidding. That's why I find it strange when they are made concerning games like this by those that think sandboxes somehow represent more character freedom or a more realistic game. Neither is true. A location railroad is still a railroad. Creating a ship where 24 beholders end up in the way of the characters is still designing encounters the characters have a chance of winning. None of it is this huge difference folks like Hemlock attempt to make it seem like.
Soon as someone reads you like to have a cohesive narrative for an adventure, they somehow think that player choice goes out the window. It doesn't. A narrative involves creating plans for NPCs in a given area. How the PCs deal with those plans is always up to the PCs. They always have the freedom to make choices including leaving. When I do what I refer to as a location adventure, I design narratives for the various enemies in the location as well even if they are not working together. All a sandbox is to me is a location railroad or a location narrative. I have done those adventures many times and enjoy them. I still like to work out motivations for my encounters whether it be a gnoll tribe or a highly intelligent king even when running location narratives. I still like to tailor a few encounters to truly challenge my group knowing they'll walk over 80% of the encounters...100% if I don't tailor a few encounters.
When I say I tailor encounters to be challenging, I do it because I have to. This idea that Hemlock has that he can just make up whatever he wants and challenge a coordinated, min-maxer party is laughable. A coordinated party runs over stuff unless you know how to challenge them. Any old monster isn't a challenge. If you're throwing things at them way above their level, then playing it poorly so they survive that is the essence of soft-balling. I don't soft-ball. If I throw a powerful dragon into an encounter, I make that dragon capable of challenging the party. It's not some random encounter they get to destroy while they chat over the table because I didn't bother to plan for tactix x, y, and z that makes the dragon a cakewalk.
Here's a question: do your PCs allow opponents to run if they can help it? I can understand them arresting someone if that is possible. Do they allow them to flee if the enemies don't have the means? Or do they pursue them to do the death unless the NPCs have the means to truly escape?
My PCs don't allow enemies to escape. I have to plan an NPCs escape if I want them to be able to escape. Meaning they have to really be able to escape like getting off a
teleport or being able to escape detection. I play NPCs the same way. My PCs know it and they have escape spells on their spell list because they know this is how I play. If a party walked into one of the encounters I expect to be challenging, they had better walk in with an escape route or they might not live.
My game is a step under killer DM. I have to be careful not create overkill encounters.
The goal is to challenge PCs, not kill them easily. No one likes that kind of game. It's discouraging. And no one likes a game where there are very few challenges or the few challenges that are in their way are easily avoidable by simply choosing not to engage. Those types of games bore people...at least they bore my players. I'm fairly certain they bore a high percentage of players. Players want to feel like they did something extraordinary. The stronger the enemy they defeat, the more satisfying the victory.