We didn't get a deep dungeon this expansion because of Bozja

[RyuDragnier]

To level an alt class it needs to be 71 min. So if you start fresh with anything, you can't touch bozja with that class until you reach the min level for it. Once inside, you would want to get earrings from it (if you don't have the preorder from shadowbringers) otherwise its a slower leveling pace. And the fastest way to do that is bring at least a level 71 tank with an essence of the irregular, a lost reflect, and taking off all your gear so you deal more reflected damage back at sprites.

The min level for it is just like the min lvl for HoH, but I don't know why you're bringing that up when you're apparently fine with HoH having it. HoH is also a slower leveling pace without the proper earrings, so again, why are you bringing that up? Fastest doesn't always mean most fun. The best way to level in PotD was to spam floors 51-60, and that was boring as hell.

Which to get the Lost Reflects and Essence of the Irregulars requires farming mobs. Once you turned in 1000 appraised items you get the earrings that makes leveling 10% faster while also stocking up your Lost Cache with potions, phoenix downs, lost reflects, auto items (reraise/potion/ether).

You can buy fragments from the market board, for really cheap I may add. Or you can exchange 1 Bozjan Cluster for 5 or 4 forgotten fragments.

And your encouraged to farm items instead of doing CE (including Castrum) anyway if you want things like Essence of the Ordained (or Profane), Lost Death, Lost Focus, Lost Slash, etc. Which if doing a bunch of prep work sounds familiar to Eureka, its not too far off.

All you really need is an Essence of the Bloodsucker/Beast/Templar and you're good to go for a lot of the place, including Castrum, since they'll help you survive easily. You're not really expected to bring anything if you're new. Lost Death isn't required for Castrum, it just makes saving the prisoners easier and faster due to the possibility of 1-shotting the guards/executioners. The prep work for Castrum is significantly less than Baldesian Arsenal as a whole.