The first problem is that more force is required to dig 48" wide verus digging 20" wide. The second problem is FELs are mostly designed to lift loads that are already loose, not dig compacted soil. The third problem is tree roots are like adding a lot of rebar to cement. Add these together, and FEL cylinders get bent.
I was pushing it to dig out the 5-6" gum tree roots with the backhoe bucket I used. Would have been a lot better to have used a larger machine with a root ripper, but I paced myself to keep digging around the stumps until they would come out. I now have some big holes in the field.