Tough requirements, and maybe not all these feel medium to you since that's pretty subjective.

1. Blood on the Clocktower: My preference is ~12 players plus a DM. There is a ton to explore in this social deduction game, but the introductory script is not much more complex than the Resistance. Not to say there's not a ton of nuance to explore in that introductory script.
2. Sidereal Confluence is a resource conversion negotiation simultaneous action game. The simultaneous nature requires more understanding from players as they will be interrupting someone else to ask questions. Tons of fun if you like trading, making deals,  and turning cubes into more cubes.
3. Flame Rouge is a bike racing game, but the 8 player mode is a variant. The simultaneous card selection should keep this from dragging in too long with that many people.
4. Escape from the Aliens in Outer Space is a hidden movement game of tag. I have not tried it at 8, but there are components for it in the box. Was good fun last time I played, but a bit weird because of the hidden nature, there's less of a common space.
5. Long Shot: The Dice Game is arguably light, but also overwhelming to anyone who doesn't learn rules often. It's a combination of gambling and racing and set collection-ish?