So regarding the Future Weapon Battles (Future Patches)

[Crushnight]

You canonically barely ever fight solo.

It's left ambiguous for the majority of fights, essentially up to the player. When the game does decide to specify one way or the other though, it's almost always on the side of the WoL having help.

I go by the reasoning of we fight solo unless stated otherwise, due to the absurd mental hoops you have to go through to try and fit other adventurers into it.

Ifrit: everyone is tied up and taken where the hell the other 3 echo users come from, hm/EX can be fine either way.

Titan: Y'shtola barely was able to send us alone and had to wait until she can strengthen it for herself to use

Garuda: we landed with just Cid and Alphinaud, how do 3 other people get through her storm barrier to joins us and disappear mid way fighting her.

Utima: actually stated to have help

Mog: either way can happen due to how to get there

Levi: again either is possible

Ramuh: challenged us on the spot with only scions around, 7 adventurers getting through the slyphlands at that time, yea no.

Shiva: Nope just solo, Ysayle never ever mentions you beat her up with people on top of how we got there I doubt 7 heretics decided to join us to take down their saint.

Nabriales: Nope no time to gather 7 people that would have to all conveniently die before we leave.

Vishap: actually stated to have help

Coils: 4 people knew about it until after it was dealt with and even then only city leaders have the knowledge outside Scions (though Ruby Weapon has just blurred this a bit but until details about it can't say anything)

That is just ARR, let alone Warring Triad/Thordan/Ravana/Nidhogg of HW, 4 lords/Lakshmi/Susano (which they actually joke about)/Tsukiyomi of SB, Titania/Innocence/Hades of ShB.

It is a lot of hoops to try and justify canonically we had 3-7 people there to help us so I tend to go story wise we do it solo but gameplay wise we do as a group.

[Jandor]

I go by the reasoning of we fight solo unless stated otherwise, due to the absurd mental hoops you have to go through to try and fit other adventurers into it.

That's fine, and you're right that some fights require jumping through hoops to justify a party, but that's not quite the same thing as them being canonically solo.

[Bright-Flower]

I'm guessing Sapphire next patch as a dungeon or solo duty boss. I'd be surprised if Sapphire was a trial over Diamond or Emerald. And we had one of the Four Lords as a dungeon boss so wouldn't be that odd.

Then Diamond and Emerald for the last two, in either order, as trials for 5.4 and 5.5.