The biggest pike I ever hooked cut through 20# fireline like a gerber knife. Know I use 50# spiderbraid and a titanium leader. Don't buy South Bend leaders.
I have a very hard time believing that a pike could bite through 20 lb. test fireline. I mean, come on, I can't do it... Maybe it was abraided some, if it wasn't well, all I can say is, you had one HUGE pike.