There's the overall wins and win% leads. But more than that, it's really the fact that Texas had seasons of zero or one loss spread out over the decades. From the teens to the 30s, a lot in the 40s, great in the early 60s, NC in '69, strong again in the 70s and early 80s, then again in the oughts.
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Florida had jack squat until Spurrier, really. '69 was a strong year, QB Spurrier's '66, and the mid-80s (when we cheated)...but Florida didn't really win anything important.
Same with Miami and FSU. The Canes were ranked here and there for a couple of consecutive years a few times over the decades, but no sustained success. No decades of truly mattering. FSU might have well not existed pre-1977.
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Then you get the Noles going on the road, taking all comers. Then the Miami NC. Then FSU finishing in the top 5 every year AND more Miami NCs. Then Florida winning NCs 3x in 12 years.
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The big 3 in FL packed 80 years of greatness into about 30 years (11 NCs in 30 yrs) altogether. And while Texas was going 9-1 off and on since 1910, the big 3 in FL were busy going 5-5 or 3-8 or 7-4...or not existing yet.