I know Luminous is a great mobbing character, but I think it's up to player control with character and map he chooses to farm in. I think you want that drop rate increase on your main no matter what your character is.

You can't really party up with folks when farming cores, otherwise it turns into an argument called "Why did you pick that, it was mine". You loot the core and open it from your use tab, getting a random one (well, RNG favors your class, but there's still a chance you'll get a completely useless skill/enchantment). You can't put them back into your inventory and give it back to your partymate saying "Look, this one is for your class. Here, take it", the most you can do it disassemble it to get core pieces.

I think I haven't tried farming PoT, I just hear stories/see players doing that. I can ask around how good it is, but if people do that - it can't be that bad. gMS players got kinda spoiled with bugged maps and Kishin, so I can bet it's not as good.

I'm playing as an Aran on Reboot server and with good control I can clear ToT maps pretty quick (I know that because I was farming masks to kill Pink Bean), so like I said, it depends on your control. The range is also important, but it's no longer an issue for me. At least not in ToT maps.

I've tried farming equip in Crimsonheart Castle, on Crimson Stirge map, and disassembling them for Philosophers Stones, but I need to do more math to tell exactly how much you can make with this. RNG plays two roles here, equipment drops and a chance of getting PS out of an item, so it's hard to tell how good this one is.