Random Encounter Difficulty

Hi.

Long story short: I'm working on an encounter table. I'm of the opinion that random encounters that serve no purpose shouldn't exist, so I am building this with the intended purpose of draining party resources between rest opportunities, and contributing to the # of fights between Long Rests that help bring class balance more in line. I also want to drive home the "dangerous monster filled wilderness" vibe of some parts of the setting.

I'm having trouble deciding whether or not difficulty should scale with the party or not, and by how much.

On the one hand, directly scaling difficulty makes the encounters more directly fit my first goal of draining combat resources and such. Every encounter would likely be fought, and each would be an appropriate challenge.

On the other hand, that feels extremely artificial, and doesn't fit the themes and vibe I am going for with my second goal. Making difficulty agnostic of player level would mean sometimes they find chumps and sometimes they have no option but to run away. This doesn't necessarily fit the first goal, though. (Also running away from fights is in a weird spot mechanically in 5e, not quite sure how to approach that in a satisfying way).

Thoughts? Ideas? Suggestions?