You're measuring success on goals scored only. There are far more measurables at play. Even having a natural striker to avoid having to play other players out of position (e.g. Son, Lucas and Dele all "leading the line" at various points) has a lot to be said for it. What we've done in the past is essentially weakening two spots in the team at the same time.
I thought Okazaki and Ulloa were highly useful players. They certainly kept defenders busy and - more importantly - allowed the likes of Mahrez and Vardy to rest when needed.
Llorente only scored a handful of goals for us, but take him out of the equation and we don't make it to the CL final. Simple as that. In fact we don't make the semi final either. He cost us £11m. The CL run brought in eight times that amount.
Arsenal are the only other "big" club who have neglected to bring in back up for their main striker and unsurprisingly they've struggled.