It happens way less often. This year's group is really good, but so were all five of those 2006 guys.
"Allgeier will end up with a better career than Brown" - better than 4,550 yards from scrimmage and 36 TDs? Absolutely no chance whatsoever. At all. Even if he does get an extra year.
And you judge the OL by (blue-goggled) NFL projections, but not the RBs, where Tonga and Fui both spent time on NFL rosters, which neither Katoa nor Allgeier will ever do. At least be consistent.