It's been a month and I'm playing other stuff now so forgive me if I get some of this wrong but if you don't want to farm a perfect spatha it might be better to take that spatha to tyrant Lugalbanda and farm bewitched Glaive: Receding Rust with like one or two good traits on it, that might be more powerful until you farm an optimal spatha. Go back and get a good one with optimal traits when you don't feel tired of farming.
Save Pharsis for when you do though, Pharsis is like top 3, or maybe top 4 bosses now they added some new ones in the definitive edition. Pros make it look easy but unless you kill her so fast she doesn't get to do anything, the stuff she does can be very difficult to deal with. If you are doing the ether blossom dance build correctly, the only bosses that should be beating you are ones with some gimmick you need to understand, otherwise you should just be melting their health bars before they or even you realize whats happening. You researched it but you think you missed something so I'll just go over the build and I might hit on something useful.
The ether blossom dance build is a super powered offensive build with only one defensive option: ghostwalker. So you master both the Duelist class and the Full Metal Jaguar class, the way dual classes work in XCX is you take the ranged weapon of one mastered class and combine it with the melee weapon of another, in this case the dual guns of Full Metal Jaguar with the longsword of Duelist. Of course you should also put useful traits on your guns/sword like "nullify ether reflect" "night vision" and some "appendage crushers" to solve a lot of problems but other than that you should just be trying to have as high potential as possible. You can get over 1000 but you'll find a lot of success with 500 or even a bit less so don't worry too much about the number just get as much as possible. So lots of potential up xx augments on your armour and some potential boost too. Since you are having difficulties, you should also get an "extend overdrive xx" augment for your armour and an "overdrive count up xx" for your weapon. Yes, that could be more potential but it's hard to overstate how useful and convenient these are, having more time to build your overdrive counter and starting with some overdrive counter already there just makes everything way easier. You can get rid of them later when you are comfortable. You also need to have more than 3000 TP. 6000 is great but 4000 or 5000 is fine. Make sure you have the right skills equipped like stuff to boost accuracy and potential and especially you want the skill core crusher which will vastly increase your total damage and you want to make sure you target an appendage at the start of each fight. Yes you can farm drops by breaking appendages without core crusher but do that in your skell, for pure, beautiful damage you want core crusher, its the reason you want ether as your damage element.
Once you have all that, each battle is mostly the same except in cases where the enemy has some special gimmick. You enter the boss battle with full TP, immediately enter overdrive and build up your overdrive count as high as you can as fast as you can. Doing this requires an understanding of how overdrive works and the effects of all the different coloured balls juggled together in combinations,
here's a video guide to understanding that fun, crazy system. "Zero zero" is a really great art to use here because it does a lot of hits so can build counter fast, but if you don't have it yet look for arts that do a lot of hits. Then at max overdrive counter you activate the offensive stance aura, and unleash ether blossom dance just like Dunban taught us. If your potential is high you don't even need a full overdrive counter for a lot of bosses.
Start practicing it with some everlasting millesaurs. You'll find you can just spam ghostwalker to avoid damage, as your counter builds up ghostwalker will recharge faster and faster. In cases with trickier enemies later you will need to know their attacks and use ghostwalker strategically. When you activate it, you're immune to all damage during the "strut" animation, then you are immune to exactly 6 hits. So if an enemy fires a volley that does 5 hits and you already avoided 2 hits, you're about to take damage, and with a high level boss it could be 1-shot, so you need to ghostwalk as that attack launches and strut through it. After you beat up some millesaurs and feel comfortable, move on to Fernando, the level 85 millesaur tyrant in Noctilum. He'll have more health and be stronger but you can beat him with the same methods. Then you move on to Luciel the Eternal, the level 92 millesaur in Primordia. I think he has a gimmick where he force topples you, so you would craft a few topple resist augments and switch them with some of your potential ups for that fight. While beating up these dinos keep an eye on their gear as these are the only guys that drop high level gravity resist armour, most other armour is weak to gravity and you could get in trouble with some bosses with gravity attacks later if you play around with builds that don't use ghostwalker. After those fights, the final and best training battle would be Gradivus the headless Emperor in Oblivia. He's only level 71, but he has the most health in the game by far so even when you shred him with blossom dance the battle will take time and require you to survive his attacks. He has multiple moves that do 6 hits so you want to watch his life bar which will announce the names of the coming moves and react to them if needed, moves like "Ether Laser" or "inferno missle" do 6 hits so you want to ghostwalk through them. He also has a gimmick where he summons a parasite which drains your TP. You need to switch targets and kill the parasite then switch back to Gradivus.
Once you beat Gradivus a few times you can say you've mastered the build. If you're having trouble with these fights, you're missing something, either how to juggle overdrive balls or maybe you don't have enough accuracy and need night vision augments or similar accuracy buffs. And remember you have to target appendages, don't just target their main body. There are many bosses with gimmicks that won't even bother you because you'll kill them so fast they don't get to use their abilities. Others will need some adjustment in augments you have equipped or a change in strategy. For example, the final boss, Telethia the Endbringer, can be a real headache when his hp goes down to 50%, he turns invincible, flies away, regens health, and does powerful attacks. But knowing this, you can just hold back, building up your overdrive counter and not using blossom dance. Then when his health is about 55%-60%, unleash blossom dance and it will kill him in seconds, he won't have time to turn invincible and fly around doing crazy stuff. It makes one of the hardest boss fights into one of the easiest. Of course if your potential stat is extremely high you won't even need that much strategy because you will completely melt him with one blossom dance when he's at full health.
