So I, too, have recently reached Abyss floor 60. 59 was a roadblock that felt pretty similar to floor 54 in terms of how important it was to know and understand the gimmick beforehand, on top of having just plain ol' good RNG rolls to boot. Floor 54 was all about focus firing the right targets (crystal -> Purrgis -> Assassin Coli), whereas 55 is about having enough durability and healing to offset Cidd's obnoxious defense down -> dual attack wombo combo, and then also being able to outright kill the dual attacking adds in the following round before they kill your entire party (having 80 souls going in really helps).
My party is, I think, pretty unusual in composition and also possibly underpowered for the floor that I'm on:
I have minimal single target damage and
no dedicated tank. Charlotte sits up front because she has the highest combination of HP and def and her lifesteal set makes it easier to top her off, but she still can't take the kinds of hits that someone like Armin, Krau, or Cecilia could. Angelica probably could take her place if I, y'know, invested in her gear and got her to 60, but I didn't, so in the back she stays. The fact that I managed to get this far with this party composition is, frankly, kind of amazing. I imagine I could have had an easier time with an actual dedicated tank and someone with high single target damage. Surin could nominally fill in this role, but I haven't gotten her to 60 and, well, I just don't have the money to upgrade her gear that much (and I hesitate to take it off of Clarissa when she's so instrumental, especially in PvP).
All of this would probably be impossible without Diene's constant healing through the rod artifact and her S2 and S3 having their -1 turn cooldown upgrades. Granted, a level 60 Angelica could solo heal pretty handily... but getting there has been a very slow process. I'll probably have her to 60 next week, but getting her gear upgraded is another matter entirely (where the fuck am I supposed to get the gold?!).
My PvP team, meanwhile, is a bit different, with Rima taking the place of Angelica:
She's instrumental to my plans, especially as an attacker, as she both lets me shut down a particularly problematic enemy target (like their strongest damage dealer or Diene if Rima manages to go first) for a turn as well as allowing me to double up AoEs with Clarissa or Charlotte, depending on the enemy team composition. There's nothing quite like blowing up the entire enemy team in the space of two turns, lemme tell ya. Given how unusual my team composition is, I'm surprised I've managed to get as far as I have. I can generally hang around the middle of challenger without too many issues, though it seems like I really need some kind of ridiculous stall composition to have a strong defense party, something I can't really remedy since I haven't rolled a single good tank since I started the game.
Speaking of rolls - Diene is still the only natural 5* I have besides Charlotte, the latter of whom I got from the initial selective summon and the former whom I got only from pity breaking (thank you, pity system!). I've been playing since day 1 and I have yet to get any other nat 5* characters. And, y'know what? I'm doing fine. I think a lot of folks are focusing too much on tiers and on-paper effectiveness and not enough on just fixing issues as they come up. Sometimes you just need bigger numbers, and that oftentimes just means investing in more gear, or getting another character to 60, or getting another awakening level, or upgrading skills a bit more.
Even with a suboptimal party composition you can be pretty successful in this game, and I like that quite a bit. Never touched the Holy Trinity (Elson aside, who was swiftly replaced with Diene) and I find any complaints about their nerfs to ring hollow in light of how far I've gotten with this setup. They were overpowered and deservedly nerfed, and the game will be healthier for it. Hopefully they keep it up going forward - and hopefully certain units aren't just straight-up immune to nerfs because rarity or some shit. We'll see how that goes.
Either way, I'm pretty damn invested in this bloody game, and I doubt I'll get its hooks off of me any time soon. Considering it's a Korean mobile game, really, I have to admit that I am still really damn impressed. We're over a month in and I'm happy to keep going. What a game!