WCI imo. Big Mom's crew were a constant threat and despite their big fails, they were heavily relevant. Apart from his Calamities, Kaido's crew just feels like a joke. Cracker and Katakuri were such intimidating foes and Katakuri was just relentless and so competent too.
The Enraged Army, Brulee and her mirror world, Big Mom's hunger rampages and her immense rampage towards the end of WCI (including the chase that went on for AGES), her homie fusion form was intense and Daifuku and Oven were such a threat at times.
I remember people jokingly or even sincerely saying Oven deserved to be a commander over his competence, which is hilariously ironic given how irrelevant Smoothie was.
It doesn't help Oda keeps making Jack constantly fail and get beaten and King not doing as much, especially compared to Katakuri too.
Orochi was a semi-decent threat at one point but that's all gone now with Kaido killing him just like that. We have 2 Yonkos in this arc and it feels less intense and dangerous than WCI somehow. It doesn't help we have Yamato now too.
If Orochi's ninjas and samurai especially were an actual threat, it would have helped. Also Denjiro not being an ally all along conveniently, but an actual antagonist.
I just feel there's so much wasted potential with Wano, the Samurai, Orochi and his forces, Beast Pirates etc. We've had BM's forces appearing since Fishman Island and making such an impressive 1st impression and being a threat through Dressrosa, (Zou if you count Capone) and WCI ofc but I've not felt the same kind of threat and danger from Kaido and Orochi's forces at all.