...i adore this depiction of moria from the one ring, plan and section both set against surrounding terrain to give a sense of scale...

I'm disappointed there's no hidden Sadam

Two that I found very easy to understand just from the battle maps were the Emerald Spire and the Abomination Vaults, as both have a central recurring feature to orient yourself by - the titular spire and the Gauntlight's beam. It makes them a lot less sprawling than many classic megadungeons, but also lets me and the players easily work out how everything connects just by comparing its position to the central feature.

If I was going to actually map one out, I'd just do it like the tube map. Point to point connections that don't correspond to real space, just nodes that indicate how each "room" or area connect. If necessary, colour code them by depth so I know when connections should involve a staircase/drop/ladder etc.

I don't map them out like this. There is a general overview, and a bunch of maps showing e.g. local caves or dungeons, but the long passages are not coveted by maps. If push comes to shove, I make something up on the spot.