My understanding is the F-15E did outperform the F16XL for the type of strike mission outlined by the competition.
It certainly out muscled it, but it also offered more flexibility as a weapons platform.

With the addition of the cranked double delta wing, and lengthened fuselage, the XL gains a lot more fuel storage, more weapons hard points, and a higher top speed.
It also loses its unparalleled dog fighting maneuverability.

The F-15E retains almost the same maneuverability as the air superiority version, (F-15C) so a flight of F-15E’s can defend themselves on egress, where the same number of F-16XL’s would require additional aircraft to provide CAP.
Probably another big factor in the decision was simply dual engine redundancy.