Until this day i still think that:
The best way for oda to make Kaido get defeated/killed in a fantastic way and without making luffy look like he is close to kaidos level yet Just because he defeated him is making kaido get some nerf that Will make sense to luffy defeat him later. Like:
-Kaido get some damage and injuries from the 5 SN in this fight but them literally destroy them and even kill Killer.
-When theres no Hope to win and they all on the ground ,Garp shows up with One admiral OR many vice admirals with him.
-Garp came knowing that his grandson would be Fighting 2 of his old enemies and knows the TRUE potencial of these 2 and that luffy wouldnt stand a chance against them both together.
-Garp fights kaido 1 vs 1 in an epic fight, while the others marines hold BM and the SN are getting treated .
-Garp fights very Well but hes not the same anymore, kaido even with damage from the fights against the scabbards and the SN manage to not only Win but kill Garp, BUT garp Will fall in a epic way , garp Will bring an entire arm of kaido with him and other smaller damages, and make onigashima fell in a place close to the capital but with no people. Garp did a Lot.
-Luffy and the others Will get up, of course not 100% but able to fight again, luffy Will get Crazy with garp death but before he do something, kid as mad as luffy with Killer death Will impale kaido with that enormous sword using All he have left and then pass out, kaido is now Very damaged, luffy fights kaido without a arm and Very injured, luffy looks better in the fight now. Kaido ask Lilin for help..
-BM seeing kaido is a goner, bettray him and take the chance to leave the arena and Go for the red Stone and leaves wano.
-Luffy defeats kaido. Kaido is on the ground, but he surprisily stands up and quickly become his dragon form to kill ALL the citizens os the capital with a boro breath, before that happens zoro comes with Emma making It Black and slice kaido Head off that Falls and destroys Orochi castle.
I would Love if something like that happened.