I have to agree with the difficulty. The Chroma Spring bosses are a massive difficulty spike compared to bosses before them. I had issues with the 2nd and 3rd bosses especially since I didn't think to use Aden's Root Crystal which has a skill that heals the party and raises attack. What doesn't help is their ATB tends to fill fast which can make untying a pain since they will likely use Subdue the moment you Struggle/Rescue since they're still Weakened unless if Seles uses Familiar Restraints with 100 Escape Level or Chelsea uses Nuh Uh (which she doesn't get to learn until Level 70) to cancel Subdue attempts. Oh, and the bosses can also inflict Stunned/Asleep (i.e., the first one has Chromatune).
The third boss also makes it worse as the player can't leave the Katoshi Isles/Shiode due to the locations on the map being disabled so if you don't have enough items and/or done sidequests like the Casino Night or Dancing Mad, the fight could be impossible without using a Story Crystal.
I believe if players mostly relied on Eileen and hadn't figured out they could also use Aden's Mud Spray (Root Crystal obtained from Casino Night) and Liliana's Rationing, they could have a hard time. It can also help that Liliana's Rationing and the Teatime from Seles' and Aden's Maid outfits are Special and are unaffected by Silence which would help with the 3rd boss as she has a powerful attack that can inflict Silence, blocking off Soothing Mist and Mud Spray. Liliana's Dancer Garb can also help especially with Speardance since each strike heals the party but getting a strike in can be annoying since the bosses tend to inflict Blind.