Relics - easily soloable and have been since pre-Adoulin, practically all 75 wins are easily soloable, possibly with the exception of Beau (chainspell+death could be tricky...), any pet job will rip the other bosses apart or any job /dnc to stun the death spell, as for farming currency, these are supposed to be the pinnicle of weapons, getting them with a week of effort really wouldn't fit.

Mythics - Only issue I see here is the six-man requirement on einherjar & possibly the spawn time on kings. Assaults/Salvage are all pretty much soloable now.

Empyreans - Not sure what you mean by needing three exactly, only issue I have with these is the plate/cinder requirement, which is only an issue as long as people aren't doing voidwatch, perhaps SE need to do something to make voidwatch more appealing to the playerbase once again. As for the farming abyssea, I've personally got six emps and solo'd them almost in their entirety as Paladin, so "requiring" three people really isn't an issue (this was actually prior to adoulin, so I'd reckon its more of a joke now than ever).