Some comments from me: (If you don't mind)
I think the Arachno badges are slightly grindy, since you don't always get Spider's Lair, so you might have to play a few games to get it.
Brick Silver requires a fair bit of luck (and probably a fair bit of grind, since you may have to try several times) because you aren't guaranteed to get the equipment you need. It's possible to get that far in the game without encountering any phase devices and even if you get them, they might not take you to the correct side of the wall. There are some pistols/shotguns/assemblies that might be able to break down the wall, but those aren't guaranteed either.
I think I would rate Arena Platinum as higher skill. The Arena is really tough at N! difficulty because as you get into the second and third rounds, the monsters from the previous rounds revive unless you have really good body disposal skills. (And it's too early in the game to have good equipment or traits for easy body disposal)
Longinus Platinum should probably be higher too. Of course, the level itself isn't that hard once you get there, assuming you have Berserker trait and a few med packs, but you have to play through 17 levels of N! to get there, which is pretty tough.
Speedrunner badges, especially UAC Diamond, are pretty grindy, since you'll probably have to try many times before you get a lucky enough game to be able to win fast enough.
Arena Diamond is highly grindy; I've tried and failed at that badge a hundred times and the only time I did it was through incredible luck.
Those are the differences in how I would rank these badges, just from a quick skim through of the list. There are probably more, but those are the ones that stand out the most for me.
I think no one would ever able to get 20-marked ones without cheating.
UAC/Demonic/Speedrunner Angelic is just absolutely impossible, at least I think.
I'm still convinced that Everyman Angelic is doable. I've failed many, many times, but I think I can do it with a lucky enough game. Now that I've got some decent recording software set up, I've been trying to record myself doing it and just the other day, I had a game where I got half-way through Deimos! I might have made it if not for the Cacodemon cave I started in, surrounded by Cacos with no cover. Some day, I'll get it; mark my words... :)
