I beat Routeless Part 3 on Normal. Clocked in at around 10 hours. I know it's not the greatest achievement as others have done it on Hard. I would place Routeless Normal as more difficult than 4 Routes Hard.
Heres my tips. Please share your own below for anyone who wants to try. Really fun challenge. I recommend people try it while they wait for the DLC.
* Early game is hard as you have no money, no world map, no materials, and no weapons. I rushed Dungeons and sold weapons and accessories I wouldn't use to grind my way out of poverty and get Eshmel into Fortress Knight to grind armour ranks. You want Healing Armour as soon as possible to get some sustain, or you will keep running out of HP and be unable to heal. Troy can help with heals. Early weapon recommendation is a maxed out Short Spear. You can find a Pilum in one of the dungeons.
* World Map: dungeons are good early. You want at least 2 Diadem Keys to get Godhand, Avatar, and Trident. The carriages in Arago and near Megaira are really important to get online. The Megaliths are also super helpful as they're good dungeons and free Warp Points. Try to snag some Agarthium to level up Zerberus. Temples are good but optional. They give Warp Points, items, and money, but require rare materials. Credna is the most important since he upgrades the spear
* Characters: Eshmel is cracked. Fortress Knight into Castle Knight with Healing Armour carries most of the game. Lategame I went Trident for White Magic. Troy is absolutely ridiculous and can solo maps. Once you upgrade Zerberus and get Modified Weapon she's good to go. Victory gem helps Troy sustain. Hong Hua really wants White Magic Treatises or Arena to get online, which is really tough since you need to repair towns. I couldn't get this going till much later. In the meanwhile she outputs serious damage with Salamander but needs babying since she is squishy. White Magic is free XP
* Gate Missions: the first few are easy but you must explore the area ahead of time so you don't burn turns trying to unlock the world map routes. Always split into 2 squads. The later gate Missions with 2-3 gates are extremely tight as they're balanced around 4-5 squads and I failed the last one by a few turns and had to retry. You really need the warp points and carriages to make it. For the multi gate ones, I had Hong Hua deal with mobs and miasma and Troy assaulted the gate on her own. For the final, I rushed the top left gate with both, took some hits on Dagsion then circled back to the middle one then bottom. Extremely tight.
* Final Mission: actually pretty difficult. I had try run around and attack gates and then Eshmel and Hong Hua would solo Balor. You need to gun down healers as soon as possible. Hong Hua can block routes with Wandering Wall. The mission dragged so long I almost ran out of Heals. But you do need to take it slow and not overcommit. For the last phase, Hong Hua can Bolting a gate if you can't reach it by movement.
Good luck anyone who tries this!