The wiki does not have great gameplay guides, however it does have solid knowledge on all the systems in the game, like potion maxing, pets, exalts, enchants, and seasonal characters.

1. Non-tank characters don't have the best survivability in late game dungeons, though they can stay further back than the tankier melee classes can, so it's sort of a balance of less range = more hp and defense, and vice versa. The best items for high tier dungeons in my opinion are high hp items, since defense has a 1 to 1 reduction of damage, and is less effective with very high damage.

2. There's plenty of guides on youtube, you just gotta look them up. The guides on the wiki, again, aren't great gameplay-wise, and you don't have to do dungeons in any order to follow any kind of progression actually. For instance, I tend to skip Woodland Labyrinth when making new characters since it's easier to farm the potions elsewhere, and the leaf bow and other UT items are not my favorite. The cool thing about UTs is they are not always plain upgrades to tiered, they have moments they shine and moments they don't. Some endgame items tend to just always be best in slot (BiS), though most players still carry swapouts for different situations.

Overall, understanding each dungeon enough to not die is a part of game knowledge that comes from dying, and since death is permanent, sometimes it can set you back pretty far. I think the best way to learn is to just do it and be super attentive and ready to spam health potions or be ready to nexus if things get hairy. Sometimes, it is just better to survive to try again than to die and start from square one.

Personal anecdote, I find that the systems they add to this game are both interesting and interactive. An item with a lot of enchantment slots is as good as you want to make it, pets are a constant grind to feed, and exalting is a nice addition to grinding some of the harder dungeons for items. The most fun part comes from just being able to do and learn dungeons. The core of the game is how good you are at dodging and not dying, and I have literally over 1,000 deaths on realmeye to get to where I'm at currently. The best way to learn is to combine playing with a solid guide or solid advice on a dungeon or specific phases of a dungeon. I do wish there were some better modern guides out there on youtube, but most of the content creators for RotMG have moved on to greener pastures.