Most event SR's don't really have good stats compared to Gacha SR's, they're still better than HR, but if you're used to Gacha SR's they won't ever compare lol, even Butler, the lowest ATK Gacha SR has like 510 ATK, but is the Tankiest Char in the game with 5.5k base HP and nearly 600 DEF. Buffers are usually the only Event Chars worth investing just cause so little Gacha units can properly buff.
I also wouldn't say the current event SR is bad or trash, looking at the wiki, she's pretty decent taking into account her All Round Stats. Most of those 600+ ATK Event chars are so squishy they would just get obliterated in most Super Boss Raids if they don't skill spam literally every turn. The fact she has a Super Strong ST Skill that DEBUFFS is alr a pretty big deal. Gacha SR ST's are either Super Strong (超特大 ) or Strong (特大 ) with Extra Effect, the difference is abt 100-104% higher % Damage multiplier depending on Skill Level. Heck, no other Event SR has a Super Strong ST. An even bigger deal is that it's 280 SP, 20 less than your usual Gacha ST's or 1 turn less to charge along with her high SP Gain (44 SP on Attack, in comparison, the Event SR ATKer with 600+ ATK 3 events ago is a Strong ST with Debuff that takes 330 SP to use and she charges it at 40 SP per attack, 9 Turns effectively). So if you even account Skill spamming, she'd still do higher DPS since her Multiplier is 700% instead of 600% and she also charges her ult faster. At a difference of 15% higher ATK when runes are accounted in, a Glass Cannon would need 7 Auto Attack turns to break even with her, since every nuke she does is 100% ATK Higher which is... oh, the same time she charges her own Ult. More if she spams due to Cyan and how much bonus Team damage her DEFENSE DEBUFF ADDS. I'd love it too if my Butler also had a Super Strong ST.
Overall, she's a pretty solid Event SR, one of the best Attackers I've seen so far. It's not super high DPS like a Gacha SR ST Attacker, but it's still pretty good damage output and survivability for a free unit.
Back in the days, sure Damage was what ppl look for as long as they had moderate defenses since Cyan abuse was a thing when it was at like 20% Chance since you'd just Skill proc almost every turn and heal back to full esp with Yukikaze/Healers. But with the nerf now making it 10%, tanking is back to being an issue and Tank stats are always welcome, esp when end of the day when you add Runes, and get to ard 700 VS 800 ATK for a Balanced Char VS Glass Cannon Event SR, it's barely 15% higher ATK for half their tankiness.
