Great to see another hobbyist who is keeping Wallago leerii.
I never experienced a problem with either my W. attu and W. leerii eating anything.
I've never had mine eating pellets etc but mine do eat makarel, trout, salmon, fresh and saltwater smelts etc. They will also eat herring on occasion.
I do keep large numbers of cichlids in the tank which they do on occasion eat as well. That shoal of 150 adult Paraneetroplus synspila has been whittled down to about 60 now.
The female took down and ate a 33" Arapaima arapaima in the spring of 2007 and I believe killed my alpha Arapaima at 71" in October of 2011. I still have one pima left at about 72" which avoids both Wallago.