i think that this is a very strong WR.
Tadese doesn't have enough speed but he is very very strong (despite his bad marathons) guy. Don't forget that he is a 26:37 10000m guy while holding "only" a 12:59 5000m PR. That's amazing endurance and he was able to replicate that for the Half Marathon.
He's also mastered the HM distance for many years before setting his first WR and then he made it better.
we all agree Wanjiru had enough talent to be a Marathon WR contender, at least a 2h03 Marathoner, and yet a prime Wanjiru produced a 58:33 so 10s slower.
I will say that Tadese was the athlete than - when at his prime - could hold the sub2h pace for longer (maybe past 30km). He is known as the most economical athlete ever.
Bekele could challenge that WR that's for sure, but I doubt he would run under 58.
Except that Bekele was a 26:17 performer, and beat ZT in XC every year but the hot one, and has never run as slow as ZTs best in the marathon. I'd say that as strong as ZT is (or was), KB is obviously faster.
The big issue here is that ZT did it while still in prime or nearly prime 10000 shape. KB is well past his 10000 best and relies on his huge strength. I'm sure he could go sub 59 if he really wanted, but sub 58:20? Doubt it.