I would argue that 8 medium encounters does not "sing" in 5E. It is likely to be tedious.
Have you ever tried running a super simple bunch-of-rooms-with-monsters, maybe a handful of locked doors and some pit traps capital-D Dungeon using straight RAW 2014 core 3 rulebooks? If you haven’t, let me tell you from experience, a lot of the design choices of 5e that seem strange or nonsensical suddenly start to make perfect sense in that context.
I suppose there may be some specific combination of 8 medium encounters that one could make "sing" but it would have to be highly curated, which means it is a lot of work.
Nah, not a lot of work. Use straight out of the book “bag of hit points with a claw and a bite attack” 2014 Monster Manual monsters, using RAW 2014 DMG encounter building guidelines. Put about 2 Easy, 4 Medium, and 2 Hard of such encounters in a dungeon with like 16 rooms, roll up a treasure hoard using the 2014 DMG rules, sprinkle about a third of that treasure across maybe 6 or 7 of those rooms, making sure most but not all of the treasure rooms have monsters or a trap in them, and put the other two thirds in a big pile in the least accessible room along with one of the Hard encounters. That design, in the words of Todd Howard,
just works.
This is to say that whatever the math says, actual fun at the table does not jive with the encounter calculator.
Fun is subjective of course. But, I can tell you from my experience, the type of dungeon I described above feels
excellent in actual gameplay, despite sounding like a snooze fest on paper.
And that is not even to ask "why do these encounters have to be in a dungeon?"
Mainly because a dungeon makes the physical structure of the fictional environment match up 1:1 with the design structure of the intended play pattern. You
could reproduce that play structure in a fictional environment that didn’t have the same physical structure, but there would be a higher risk of it feeling forced, because there wouldn’t be literal walls keeping the players within the intended structure.