A big part of it is 4 years in an era where very few All Americans even play 3 years. Here's another way to look at it:
A year one: 14.9 pts, 47%fg, 6.7 rebounds, .6 assists, 1.1 steals, .9 blocks
A year two: 18 pts, 45%fg, 7.6 rebounds, 1.1 assists, 1.0 steals, .8 blocks
A year three: 22.8 pts, 58%fg, 7.7 rebounds, 1.1 assists, .8 steals, 1.1 blocks
---Goes top 5 NBA
B year one: 12.1 pts, 56%fg, 6.4 rebounds, 1,1 assists, .3 steals, 1.0 blocks
B year two: 13.1 pts, 53%fg, 4.5 rebounds, .9 assists, .3 steals, .5 blocks
B year three: 23.9 pts, 54%fg, 9.8 rebounds, 1.2 assists, .8 steals, .1.8 blocks
---comes back for 4th year because of quirky skill set where no other players of this era with that production do
Does playing four years matter? Yes. Does that make him "the greatest player by far to ever step foot on a court in this state? No. It's really clear that his year by year production was not any more impressive than Fizer's, ton of bold there for Fizer and most where he didn't lead are very close.
Also need to note that Fizer's teams were slow paced teams. Fizer's points per ISU posession probably absolutely destroy Luka's points per Iowa possession. I'm guessing Luka's teams all averaged more points per game than Fizer's last team that finished ranked #3.