2 points ->
1) Xebec even after killing an Admiral had more than enough strength to clash on equal terms with Harald .... a clash which oliberated everything in a 5km radius. An equal clash portrayal wise but Xebec had just killed an admiral before clashing vs Harald and obviously this Xebec hasn't even formed Rocks pirates yet so even this is not Peak Xebec. That is saved for God Valley. Bonkers !!
In the few years that he stayed in Elbaf....hopefully it gets revealed later that Xebec tried to enter or reached Heaven realm of Elbaf and met whoseover the present God of Elbaf is.
2) Ancient weapons , entire Elbaf army , entire Giants army , Yamato , Marco , Old Rayleigh & Gaban , Boa , Joyoboy level Luffy and his PK level crew and innumerably strong allies would be needed to bring down Imu. Plus something like eternal flame and obviously the knowledge of 1st and 2nd world are all prerequisites to be able to fully understand the enemy we are up against.